"You see the flash and it sounded like a bomb (went off) exactly at the same time. It was so loud," said Steve Peddle, who was with his wife inside the main tent of the inaugural Whitby Ribfest when the lightning hit around 2 p.m.
"All of a sudden, like not even three seconds after that, you started hearing people screaming."
Officials said none of the 17 taken to hospital suffered life-threatening injuries, but many at the event were shaken by the incident.
"It wasn't just one person — there was a lot of people screaming. And so you knew somebody must have got hit," said Peddle, who travelled from nearby Pickering with his wife Rose.
"I looked over and where my wife had been sitting before we got our ribs... there was three people lying on the ground there."
Another festival-goer, Michael Thompson, said a huge crowd of people had flooded into the large white tent moments before the strike as rain pounded the festival grounds at Iroquois Park in Whitby, which sits some 55 kilometres east of Toronto.
"It was pretty chaotic. We didn't really know what was going on," the 45-year-old said of the immediate aftermath of the strike.
"Some first aid people were in there and they (were) pretty quick when they rushed in. They were throwing tables out of the way so they could reach the injured."
Durham police said those who were injured were quickly taken to local hospitals.
Nine people were rushed via ambulance to Lakeridge Health in Durham, some suffering from minor burns, while others were uninjured but want to be checked up on, said a spokesman with the hospital.
"Everyone who came, nobody had anything serious. Everybody has been discharged," said Aaron Lazarus.
Whitby Ribfest chairman Colin O'Regan said the festival didn't see the lightning storm coming before the bolt hit the tent.
"Basically a sudden storm came out of nowhere," he said.
The festival's emergency plan — drawing on lessons learned from other rib festivals — ensured first aid workers were able to race inside the tent "within seconds," while other staff and police already at the event kept the crowd orderly, O'Regan added.
Additional police, fire and emergency officials arrived minutes later, he said.
The Durham Region, which includes Whitby, was put under a severe thunderstorm watch hours before the strike.
O'Regan said emergency officials who were already at the festival had been monitoring the thunderstorm watch.
"We were aware but felt that there was no risk to the patrons attending," he said.
No heavy rain or any other indication the storm was coming was noticed until minutes before thunderclouds rolled in and lightning struck the tent, he said.
There were several thousand people attending the festival when the strike took place and many more were expected to show up later in the afternoon, O'Regan said.
"It occurred earlier in the day when we were not as populated as we would have been," he said, noting that thousands had attended on each of the two previous festival days.
— By Will Campbell in Toronto
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