A transformer fire at a BC Hydro's Atchelitz substation just east of Abbotsford left tens of thousands of people without power this morning.

Up to 30,000 homes in Abbotsford and Chilliwack were without power and thousands could remain so until later in the afternoon, according to B.C. Hydro.

The fire started shortly after 9 a.m. and the substation was shut down so firefighters could attack the blaze safely, BC Hydro stated in a noon press release

Black smoke could be seen billowing from the site this morning.

Power for most Chilliwack customers was restored quickly, but customers Sumas and Atchelitz areas remain without power, according to BC Hydro.

Abbotsford Fire Rescue Service Deputy Chief Mike Helmer said that an explosion was reported at the site, and AFRS provided the Chilliwack fire department with some foam and a training officer to supervise the use of the substance on the blaze.

"It's quite a major incident," said Helmer, adding that the AFRS got calls from concerned residents in the area.

"As the neighbouring community, Chilliwack department will contact us if there are any air quality issues but we haven't got an update yet."

The fire is in a rural area with a low population and the AFRS will contact area residents if there is any danger, he said.

At 12:33 p.m., the City of Chilliwack declared the fire was out.

However, it cautioned the transformer and its storage tank - which held 40,000 litres of oil - could still re-ignite.

Chilliwack officials continued to urge the public to stay indoors and stay away from the smoke.

Employees at the substation are safe and accounted for, with one person transported to hospital as a precautionary measure, reported B.C. Hydro.

The cause of the fire is undetermined.

A spill response team is en route and an environmental assessment team will also investigate.

The Atchelitz substation serves approximately 50,000 customers and is located on farmland near the intersection of Lickman Road and South Sumas Road.

- with files from Chilliwack Times