Three people were killed in a crash in Alliston, Ont., about 90 kilometres north of Toronto, which was reported to police at about 8 a.m. on Sunday.
Police say the deaths resulted from a single-vehicle rollover on the Adjala Tecumseth Townline between the 10th and 11th lines. The names of the victims have not yet been released.
OPP Const. Kelly Daniels-Griffis said it is believed the vehicle struck a cement bridge before going into a rollover and coming to rest upside down in a ditch.
"We do have a deep ditch here, it’s sort of a run-off from an agricultural field," Daniels-Griffis told CBC News during an interview on Sunday.
She said police were still trying to determine if weather was a factor in the collision.
Earlier in the morning, an OPP detachment in Whitby, Ont., received a report about a single-vehicle collision in a ditch along Highway 401.
Police were told that another driver stopped to help the person whose vehicle had crashed, who was subsequently seen walking in the direction of Bowmanville, Ont., after the collision.
The OPP then received another call from a tractor-trailer driver who believed he had struck a pedestrian in the eastbound lanes of the highway in the Township of Clarington.
A 49-year-old male was pronounced dead at the scene. His name has not been released.
In York Region, police were still investigating a suspected hit-and-run that left a pedestrian dead in Markham, Ont., on Saturday.
Tweets from the York Regional Police account indicate that Kennedy Road was closed between Denison Street and Gorvette Road following the fatal collision.
OPP Sgt. Dave Woodford said the number of deadly collisions on the roads was an indication that drivers must be aware of the conditions around them.
"It’s been a tragic weekend," Woodford said in a telephone interview with CBC News on Sunday.
2 deadly crashes on Highway 10
North of Toronto, deadly collisions happened on back-to-back days on Highway 10.
The first fatal crash occurred late Friday afternoon, when a car collided head-on with a pickup truck between King Street and Boston Mills Road.
The pickup truck driver was hospitalized as a result of the crash, while the driver of the car was killed.
Police identified the deceased as Howard Hughes, a 50-year-old firefighter who was driving to his home in Orangeville, Ont., at the time of the crash.
Hours later, police said another head-on crash occurred on Highway 10 when a southbound pickup truck crossed the centre line and struck a delivery truck on Saturday morning.
The Saturday crash occurred just a few kilometers north of the deadly crash that occurred the night before.
The pickup driver was killed. Police have identified the victim as 37-year-old Adam Syrnyk of Barrie, Ont.
In southwestern Ontario, a male pedestrian was struck and killed Saturday night near a QEW ramp at Dunkirk Road in St. Catharines, Ont.
A news release from the Niagara Regional Police said a man driving a Pontiac Grand Am was attempting to turn on to the QEW when a 59-year-old male pedestrian was struck around 8:15 p.m.
The victim was pronounced dead at the scene. The collision remains under investigation.
Earlier on Saturday afternoon, a pickup truck left a roadway and struck a hydro pole in Blandford Blenheim Township.
The vehicle’s driver was rushed to a hospital in Woodstock, Ont., where he was pronounced dead. His name has not yet been released.
A male passenger survived the crash and was treated for non-life threatening injuries in a Kitchener, Ont. hospital.