A fire at a house in Hamilton is now being treated as suspicious.

It broke out just after 5am at a property in Tamahere Drive.

Fire Service shift manager Scott Osmond said it's a small house next to the new Waikato Expressway, which is vacant.

He said it was well alight when crews arrived but there was no one inside.

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Osmond said the fire's now out and there's a fire investigator looking at the cause.

He said he's identified something suspicious so police have been called.