Country Fire Authority operations officer Peter Bell said a wood heater was the cause of the blaze.

"The fire started in the wall behind the heater," he said.

"It went up into the ceiling and the ceiling was extensively damaged.''

The fire also caused significant damage in the roof and wall.

Mr Bell said four brigades and 20 fire-fighters took about 40 minutes to bring the fire under control.

He said the fire started about 4.20am.

Mr Bell said the fire activated the couple's smoke alarm, which was crucial to their escape.

He encouraged people to be safe.

"Make sure in all heathers - especially wood heaters - flues being cleared out and professionally installed and make sure you've got a working smoke alarm," he said.

"Don't put clothes directly in front of open fires. Make sure they're a good metre or further away from an open fire.

"Make sure there's a guard around the open fire so no embers can come out."