A Sydney father says he feared for his baby son as a fierce fire engulfed five cars and several trees in a street in the city's eastern suburbs early this morning.

Police said emergency services were called to Birriga Road in Bellevue Hill shortly before 5:00am on Monday, responding to a report that five cars were on fire.

Four cars were destroyed by fire at Bellevue Hill in Sydney's east. ( Supplied: Guy Beynon )

Shay Zakhaim said the waking up to the cars burning was frightening.

"It was pretty scary, it was a big fire, the gas tanks kept blasting," Mr Zakhaim said.

He said the fire was also quite high, spreading to nearby trees.

"My baby boy sleeps here in the front room, so I grabbed him, moved him to the back of the house first thing, then went out to have a look.

"The firefighters put it out pretty quickly."

Police said the fire originated in a four-wheel drive that was parked in the driveway of a house and then spread to four other vehicles parked nearby.

The four-wheel drive and three cars were destroyed while another car sustained minor damage.

Rose Bay police Acting Inspector Michael Capon said the cause of the fire was not known and officers were treating it as suspicious.

"All fires are treated as suspicious until we can prove otherwise," Inspector Capon said.

"Fires like this are dangerous to the public and we are grateful no-one was hurt in this instance."

A witness said he heard a bottle break before a four-wheel drive caught fire in Bellevue Hill.

He said investigators were doing a full canvass of the area and would be looking into whether there was CCTV available in the area.

"We are asking for witnesses or anyone who has any information about this fire to come forward and contact Rose Bay police or Crime Stoppers."

Guy Beynon said he called emergency services when he saw the car go up in flames.

"I heard a bottle or something break and then I looked out my window and I saw a car on fire, which quickly spread to a second car," Mr Beynon said.

"I rang triple-0 and then my wife rang triple-0 after it spread to a third car, and then five cars are all lit up, and a tree."

Mr Zakhaim said his car did not suffer substantial damage in the blaze.

"It's only my tyre, seeing the other cars I think I am the lucky one," he said.