Damages from the flooding brought by a severe thunderstorm that struck Canada's Toronto on July 8 have been so far dubbed the costliest for the province's insurers.

Initial estimates released on Wednesday by the Insurance Bureau of Canada said claims for damages have reached more than $850 million from the lone incident alone. Insurers expect the number to still grow as more claims get processed.

"[In] the last four years prior to this, damages have been running at or above a billion dollars for the country," Steve Kee, director of media relations with IBC, said. "This is $850 [million] on just one shot. We still have a half a year to go."

The Downtown East Village neighbourhood of Calgary, Alberta, during the 2013 Alberta floods (June 21, 2013).

The current figures overtook a $650 million cleanup bill from a wind and rain storm that struck the same province in August 2005.

"While these preliminary estimates are staggering, we do expect them to go even higher," Ralph Palumbo, IBC vice president for Ontario, said in a statement. "The good news is that our industry was well prepared to handle our obligations to customers."

He also said that such occurrences might already be considered by the members as the present reality.

"Damage caused by more frequent severe weather is just another situation our members must prepare for. The Ontario government is urged to acknowledge this and to exercise caution when it comes to imposing auto insurance premium and return-on-equity reductions without first introducing reforms that will reduce costs in the product. Without such savings, the government is almost certain to make a bad situation worse, ultimately for consumers," Mr Palumbo said.

The early July severe thunderstorm gave off a record rainfall of 126 millimetres on Toronto, provincial capital of Ontario and Canada's largest city, in just a two-hour period. A power outage ensued, affecting 300, 000 residents and forced down subways. About 1,400 passengers were stranded for hours on a commuter train filled with water.

The torrential rains likewise washed out sections of track across the GO Transit rail system, causing numerous delays and system shutdowns. Both Toronto Pearson International Airport and Toronto Island Airport reported significant delays and cancellations.