A barking dog alerted a family to a fire started by a hot water cylinder in Levin today.

The fire started about 1.30am at the Winchester St home.

Chief fire officer Lindsay Walker said the dog started barking and woke up the occupants, a husband and wife, their daughter and an elderly man.

Smoke alarms also went off and the family evacuated and called the fire service.

Mr Walker said there was substantial damage to the area around the gas hot water cylinder.

The house was also smoke-logged.

Firefighters spent an hour putting out the fire and then dampening down hot spots, before ventilating the house.

The fire may have been caused by something resting on the hot water cylinder, Mr Walker said.

A fire safety officer was investigating.

- © Fairfax NZ News