The Don Valley Parkway has reopened after heavy overnight rain caused a shutdown of the southern portion of the Toronto highway.

Meanwhile, Environment Canada is investigating damage in Brampton, Ont. after high winds downed trees and tore the side off one building.

The heavy rain that hit the GTA overnight caused water in the Don River to cascade onto the Don Valley Parkway, where large sections of the highway were flooded.

The southern end of the Don Valley Parkway from the Gardiner Expressway north to Bloor Street was closed at about 5 a.m. Wednesday as waters continued to rise -- in some areas even reaching above the guardrails.

Police opened the southbound lanes of the roadway to traffic shortly after 9:30 a.m. and the northbound lanes opened about 40 minutes later.

Mayor Rob Ford said Wednesday afternoon city crews moved “quickly and decisively” to minimize the flooding impact.

“This could have turned into a nightmare but it did not,” Ford told reporters during a brief press conference at city hall.

Crews are monitoring the situation “very closely” as there is a risk for more rainfall Wednesday afternoon and will alert the public should any new issues arise, Ford said.

Toronto Const. Clint Stibbe of traffic services said Wednesday’s flooding is the worst he has ever witnessed.

“The most I’ve ever seen is five lanes of the Don Valley flooded. We’ve got six lanes flooded plus the ditches as well,” he said. “It’s a substantial amount of water.”

With a major portion of the Don Valley Parkway closed, drivers faced a slow Wednesday morning commute.

Hours after police had shut down the Don Valley Parkway, the driver of a minivan managed to makes his way onto the roadway.

The van, the only vehicle on the southern end of the highway, was captured on camera attempting to navigate the flooded roadway, before turning around and driving in the opposite direction.

Meanwhile, a portion of the GO Transit Richmond Hill line remains closed after flood waters submerged a stretch of tracks west of the Don Valley Parkway, shuttering service to Oriole and Old Cummer stations on the Richmond Hill line.

Flooding has also been reported on the Bayview extension between Pottery Road and Rosedale Valley Road.

West of Toronto, in Brampton, Environment Canada is investigating heavy winds that caused damaged throughout the community.

Streets in the city’s downtown were littered downed trees and broken tree limbs, while the wall of an unoccupied warehouse collapsed.

Environment Canada issued a heavy rainfall warning the Greater Toronto Area overnight, as rainfall amounts were expected to reach up to 50 mm. The warning was lifted at around 5:30 a.m.

A risk of thunderstorms was forecasted for Wednesday as temperatures in Toronto were expected to reach 25 C.