A home north of Greymouth has been extensively damaged in an early morning blaze.

A Fire Service spokesman said the two-storey house was engulfed by fire when crews arrived at the property on State Highway 6 just after 3.10am.

"We got there pretty quickly and discovered a family home well involved in fire," he said.

"The house is extensively damaged."

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A family inside the house escaped without injury.

Firefighters remained at the property this morning damping down hot spots.

A fire safety officer would investigate the cause of the blaze, the spokesman said.