MISSOULA, Mont. -

The Missoula Fire Department knocked down an apartment fire near downtown Missoula Sunday night.

A witness told NBC Montana the alerted to the blaze after someone knocked on his door and asked him to call 911.

 "I was sitting at home, doing nothing and someone started knocking on my doorframe,” said Missoula resident John Maas, who lives in the same apartment complex. “I opened it up, she said there was a fire, could you call the cops for me. So I called them, I hit the fire alarm, and there was just a bunch of smoke coming out the A1 apartment."

Maas said the 2 residents of the apartment – a woman and her son- were able to escape without injury.

Fire officials said they were called to the blaze around 6 p.m., and found heavy smoke coming out of a basement apartment on 329 East Front Street.

Officials say crews were able to keep the blaze contained to the single unit. They said the main damage was in the kitchen.

Witnesses said the resident told them she was heating oil on the stove, when it suddenly ignited and quickly spread.

Fire officials confirmed the blaze started in the kitchen. They said it caused an estimated $20,000 worth of damage.

Officials say they’re still investigating the cause.