A neighbour helped a Wangaratta mother and her two young children flee their Burke Street unit after fire took hold on Tuesday morning.

The man said he heard the smoke alarm activate, and then the mother's screams, shortly after 11am.

"I ran into the unit which was filling with black smoke and helped her and her two toddlers get out of the home," he told the Wangaratta Chronicle.

"We then got the dog in the rear yard free.

"She had called triple zero and the firefighters were here within five minutes.

"Thankfully no one was injured."

Fire Rescue Victoria Wangaratta station officer Robert Skase attending on-scene said the fire is believed to have started in a rear bedroom and spread into the roof cavity.

He said fire crews wearing breathing apparatus had the incident under control within about 10 minutes.

"We were able to contain the fire mainly to the rear bedroom, but the unit had sustained a lot of heat damage," he said.

The cause of the fire remains under investigation.

FRV officers were supported by CFA volunteers from Wangaratta and South Wangaratta brigades.

Ambulance Victoria paramedics, together with power and gas company representatives were also on scene.