Sydney, Mar 15 (IANS): A fire at a boarding house in Sydney has killed three people, with another in critical condition, the police said on Tuesday, saying that the cause of the blaze is of "suspicious" nature.

Firefighters were called to a two-level boarding house in Newtown, a suburb in Sydney's inner west, early Tuesday morning, reports Xinhua news agency.

Firefighters said it took about two hours to get the blaze under control.

A body was recovered from the rubble in the morning with two more uncovered in the afternoon.

Police said there were also "serious concerns" for a fourth person who escaped the fire, and is in a "crucial condition" at central Sydney hospital.

In a statement, New South Wales Police Assistant Commissioner Peter Cotter said the incident was being investigated as a murder.

"We are treating this as suspicious - it was an explosion, the flames took hold extremely quickly," he said.

"It would be fair to say some type of accelerant was used - we are treating this as a murder, we are treating this as a maliciously lit fire."

Residents in surrounding buildings have been evacuated due to instability in the boarding house after the fire.