Meteorologists and health authorities are once again urging residents in British Columbia's South Coast to take precautions on what could turn out to be the hottest day of 2018.

"We’re going to be flirting with a lot of records," Environment Canada meteorologist Matt MacDonald told CTV News Wednesday. "I would expect about a dozen or perhaps even more to fall across the southern half of the province."

Temperatures reached the mid-30s in inland communities such as Hope, Abbotsford and Chilliwack, triggering a heat warning from the agency that covers the entire Lower Mainland as well as much of Vancouver Island and the Southern and Central Interior.

Closer to the coast, daily highs peaked just below the 30 C mark.

“This is actually our fifth heat wave this summer," MacDonald said, adding that the region can expect similar temperatures until at least Friday.

The heat warning is accompanied by an air quality advisory for the eastern part of Metro Vancouver and the Fraser Valley due to high concentrations of ground-level ozone, which forms when pollutants emitted by burning fuel and organic compounds from solvents react in the presence of sunlight.

In both cases, officials are encouraging residents to spend as much time as possible indoors, preferably in an air-conditioned environment.

“Just try to stay inside or out of the sun during those peak hours which is noon until about 6 p.m.,” MacDonald said.

For some, however, that kind of reprieve simply isn't an option.

Roofer Mardo Bagayan told CTV temperatures are so high they are causing the asphalt shingles he works with to melt.

"Because you’re facing the roof, the asphalt it heats up and then it's reflecting in your face," he said, adding that it is between 5 and 8 C hotter up on the roof than it is on the ground.

He and his crew members are trying to stay cool by taking more frequent breaks, staying hydrated and working shorter hours, but he remains "especially worried about heat stroke."

Environment Canada says infants, the elderly, pregnant women and those with pre-existing conditions such as asthma are particularly prone to heat-related illness.

The agency is also reminding residents to check on neighbours who live alone and to never leave children or pets inside a parked vehicle.

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With files from CTV Vancouver's Allison Hurst