Yvette, who declined to give her surname, said she was cooking in her kitchen about 6.30am on Sunday when she saw flames just outside her window.

"I could see the fire out the back and it was literally moments, it just got out of hand," she said.

"The next thing I knew, I looked out the front and all the neighbours were out and people were evacuating because we've got a lot of kids in the area."

Emergency services were called to the home in Kooyong Road at Riverview, near Lane Cove, shortly after 6.30am, following calls from neighbours saying the home was well alight.

The two-storey brick home, which is surrounded by thick bushland, was completely destroyed and neighbours had to be evacuated, police said.

The home owners, Michael Dadd, 75, a retired research scientist at CSIRO, and his wife Amanda, 70, died in the fire. The couple had been married for 50 years and had adult children and grandchildren. In 1999 Mr Dadd was made a life member of the Australasian Society for Ultrasound in Medicine.

"A crime scene will be established when it is deemed safe for investigators to enter the home," police said on Sunday morning.

Another neighbour, Karen Ryan, said the couple's next-door neighbour, Mark, tried to rescue them.

"So he went next door and for some reason the keys were in the outside of the front door so he opened the door... but there was smoke everywhere," Ms Ryan said.

"He was going in to see if he could find anyone because he was concerned, then the flames just took over. The hallway was filled with smoke."

Yvette said there was an explosion just before firefighters knocked on her door to evacuate her and her 15-month-old son.

"There was a lot of flames, it just got bigger and bigger," she said.

Yvette said the two who died were "a lovely couple".

NSW Fire and Rescue Inspector Steve Moran said it was a "very substantial fire" and a difficult job for emergency services professionals.

Police will prepare a report for the coroner. A faulty electrical appliance is suspected as the cause of the fire.