Heavy rainfall is complicating work to restore power across British Columbia’s lower mainland, as crews work to reconnect thousands of people who have been without electricity for two days.

Environment Canada issued a rainfall warning for Metro Vancouver, the Fraser Valley and Howe Sound on Monday. Northern parts of Vancouver and Fraser Valley can expect up to 50 mm of rain, while amounts in Howe Sound may reach 80 mm, the weather agency warned.

According to BC Hydro, an estimated 35,000 customers in Lower Mainland were still without power on Monday afternoon. 

Crews have been working to restore power across the Vancouver region since a windstorm downed power lines, uprooted trees and caused damage across the city on Saturday.

The storm damage and power outages are centred in Burnaby, Surrey, Coquitlam and Langley.

In Vancouver, the majority of homes and business have had their power restored, deputy city manager Sadhu Johnston told CTV News Channel.

All municipal facilities, including city hall, have power, he said.

“This will go down in history as probably the first summer that Vancouver really felt climate change and all those impacts,” Johnston said.

He said the extreme drought Vancouver and surrounding areas experienced in the summer made trees vulnerable to the “freak windstorm” over the weekend.

He added that it could be weeks, “if not months,” before the full cost of the clean-up efforts is known.

BC Hydro said it brought in more than 440 people to work on restoring power in affected areas, including crews from Prince George, Smithers, Terrace, and Vancouver Island.

"We’re continuing to make great progress," BC Hydro spokesperson Simi Heer said Sunday afternoon. "We’re getting thousands of customers’ (power) restored each hour. Crews are out there and they’re working as hard and quickly and safely as they can."

She said damage caused by the windstorm is "varied and extensive."

"This is one of the worst storms we’ve seen for this region in years," Heer said. "It’s unprecedented damage."

Officials said it could take weeks for city crews to clean up the debris left behind after the storm.

In addition to the property and infrastructure damage, a woman in her 40s is in hospital with life-threatening injuries after she was struck by a falling tree while walking with her daughter in Surrey.

So far, no other cases of serious injury have been reported as a result of the windstorm.

With files from CTV Vancouver