Thousands remain without power in Toronto and Mississauga after massive thunderstorms slammed the city Monday with record rainfall, flooding transit systems, homes and even highways.

UPDATE: Toronto Hydro says it is "at capacity" with its supply of electricity provided by Hydro One.

The company added that, at Hydro One's request, it will begin "load-shedding" or rotating blackouts in specific areas in order to conserve energy.

The affected areas are:

Toronto Hydro says there are now 50,000 customers without power, up from the previous estimation of 20,000.

At the height of the outage, between 400,000 and 500,000 people in the GTA were without power, according to a Hydro One press release.

Hydro One repair crews worked overnight, reconfiguring the "GTA electricity system to restore power to as many people as possible," a Tuesday press release states. There is potential for further outages as the system is not yet stabilized, the release adds.

As of 8 a.m. Tuesday, around 20,000 people remain without power mostly in the GTA's west-end, specifically "in the areas bounded by Dundas Street South to Valermo Drive; The West Mall East to Stephen Drive, and Ormskirk Avenue south to The Queensway; South Kingsway East to Windermere Avenue," according to Toronto Hydro.

Customers who don't live in the GTA's west-end but have outages should call Toronto Hydro's Lights Out line at 416-542-8000 and file a report.

A full map of outages in the GTA from Hydro One shows the areas affected.

An Enersource map of Mississauga shows that most of the city's power has been restored, but residents can check back for updates as repair crews continue working.

Enersource said that most, if not all, Mississauga residents should have power back Tuesday, according to CTV News.

Toronto residents can see what areas are without power with Toronto Hydro's map.

TTC service has been restored, except between Jane and Kipling stations, the Toronto Star reports. Shuttle buses are available.

Toronto Hydro is asking customers to conserve electricity as its crews continue repairs, and in a press conference Tuesday Rob Ford did the same, adding the hydro system “is hanging on a thread," the Globe and Mail reports.

Toronto Hydro’s president Anthony Haines asked customers to help with "load-shedding" to reduce strain on the system.

Ford also said he has asked for a review of the city's emergency response system, adding that while many things "worked well last night,” many areas such as communicating information could have been improved.

Also on HuffPost:

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  • In this photo provided by Michael Li, water rises in a GO Train stranded on flooded tracks in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/Micheal Li via The Canadian Press)

  • Stranded passengers await rescue on a flooded GO Train in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Frank Gunn)

  • A GO Train is stranded on flooded tracks in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Winston Neutel)

  • A GO Train is stranded on flooded tracks in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Winston Neutel)

  • A tow truck driver floats a car out of the Don Valley Parkway in Toronto on Monday, July 8 2013. (AP Photo/The Canadian Press, Frank Gunn)

  • A woman gets back into her flooded car on the Toronto Indy course on Lakeshore Boulevard in Toronto on Monday, July 8 2013. (AP Photo/The Canadian Press, Frank Gunn)

  • A woman gets back in her car in flood water on Lakeshore West during a storm in Toronto on Monday, July 8, 2013. (AP Photo/The Canadian Press, Frank Gunn)

  • Stranded passengers are rescued from a flooded GO Train in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Frank Gunn)

  • Stranded passengers are rescued from a flooded GO Train in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Frank Gunn)

  • Stranded passengers are rescued from a flooded GO Train in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Frank Gunn)

  • Stranded passengers are rescued from a flooded GO Train in Toronto on Monday, July 8, 2013. A severe thunderstorm forced the shutdown of Toronto's subways, cut power to 300,000 in Canada's largest city and caused Porter Airlines to cancel all flights out of the downtown airport Monday evening. (AP Photo/The Canadian Press, Frank Gunn)

  • Toronto Apocalypse 2013

  • After the storm cleared, traffic heads out west of the downtown core.

  • Toronto Apocalypse 2013

  • Toronto Apocalypse 2013

  • Toronto Apocalypse 2013

  • <a href="https://twitter.com/meltait/status/354380494454001664" target="_blank">Tweet from @meltait</a>

  • <a href="https://twitter.com/hungrypo/status/354382745381789696" target="_blank">Tweet from @hungrypo</a>

  • <a href="https://twitter.com/TeenainToronto/status/354399592109993985" target="_blank">Tweet from @teennainToronto</a>

  • <a href="https://twitter.com/Nock4Six/status/354362607794270209" target="_blank">Tweet from Nock4Six</a>

  • <a href="https://twitter.com/weathernetwork/status/354416176895500290" target="_blank">Twitter: Tweet from @weathernetwork</a>

  • <a href="https://twitter.com/joyandwoe/status/354376407238971394" target="_blank">Tweet from @joyandwoe</a>

  • <a href="https://twitter.com/mathewi/status/354377501700669441" target="_blank">Twitter</a>

  • <a href="https://twitter.com/dorkkly/status/354384348629323776" target="_blank">Tweet by @dorkkly</a>

  • <a href="https://twitter.com/robcer/status/354366213209600003" target="_blank">Tweet by @robcer</a>

  • <a href="https://twitter.com/sabrina_scott/status/354358458629369858" target="_blank">Tweet by @sabrina_scott</a>

  • <a href="https://twitter.com/astroboy/status/354390796469944320" target="_blank">Tweet by @sukminc</a>

  • Flood

    Sent to us by <a href="https://twitter.com/MsNikkiThomas" target="_blank">@MsNikkiThomas</a>

  • <a href="https://twitter.com/Lucypalm/status/354369513317351427" target="_blank">Tweet by @lucypalm</a>

  • <a href="https://twitter.com/jumpnhigh/status/354390010704822272" target="_blank">Tweet from @jumpnhigh</a>

  • <a href="https://twitter.com/vickilaszlo/status/354381014333808640" target="_blank">Tweet from @vickilaszio</a>

  • <a href="https://twitter.com/DSCanCreations/status/354410559065706496" target="_blank">Twitter</a>

  • Dave Pankew

  • Dave Pankew

  • Lakeshore and Spadina.

  • Union Station Tuesday

    <a href="http://www.huffingtonpost.com/social/hp_blogger_Kenny Yum"><img style="float:left;padding-right:6px !important;" src="http://s.huffpost.com/contributors/kenny-yum/headshot.jpg" /></a><a href="http://www.huffingtonpost.com/social/hp_blogger_Kenny Yum">HuffPost Blogger Kenny Yum</a>:<br />A little wet on Tuesday morning.

  • Flood

    <a href="http://www.huffingtonpost.com/social/hp_blogger_Kenny Yum"><img style="float:left;padding-right:6px !important;" src="http://s.huffpost.com/contributors/kenny-yum/headshot.jpg" /></a><a href="http://www.huffingtonpost.com/social/hp_blogger_Kenny Yum">HuffPost Blogger Kenny Yum</a>:<br />Near Kiping Station Monday after 6 p.m.

  • Flood

    Sent to us by <a href="https://twitter.com/MsNikkiThomas" target="_blank">@MsNikkiThomas</a>

  • Flood

    Sent to us by <a href="https://twitter.com/MsNikkiThomas" target="_blank">@MsNikkiThomas</a>

  • The Storm

    <a href="http://www.huffingtonpost.com/social/MaryHynes"><img style="float:left;padding-right:6px !important;" src="http://s.huffpost.com/images/profile/user_placeholder.gif" /></a><a href="http://www.huffingtonpost.com/social/MaryHynes">MaryHynes</a>:<br />Another shot from the subway

  • After the storm @ Union Station

    It's like the rain never happened

  • The Storm

    <a href="http://www.huffingtonpost.com/social/MaryHynes"><img style="float:left;padding-right:6px !important;" src="http://s.huffpost.com/images/profile/user_placeholder.gif" /></a><a href="http://www.huffingtonpost.com/social/MaryHynes">MaryHynes</a>:<br />From the Viaduct

  • NEXT: Toronto wants Calgary Mayor Nenshi

    As the City of Toronto dealt with flooding on Monday, some Twitter users wondered about Calgary Mayor Naheed Nenshi's availability. <a href="http://www.huffingtonpost.ca/2013/07/08/toronto-flooding-2013-naheed-nenshi_n_3564081.html" target="_blank">READ THE STORY HERE</a>