At least three people have been killed and three others have been injured when flames tore through a boarding house in Newtown.

Fire crews are battling spot fires and structural issues as they look for people who are unaccounted for.

Assistant Commissioner of the NSW Police Peter Cotter told Jim Wilson the fire is being treated as a murder investigation.

“We are treating it as a very serious crime.

“We understand that there are another three that still lay in situ.

“This was some type of targetted attack.”

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Nine news reporter Lauren Tomasi told Deborah Knight there is a grave concern for a fourth person believed to be inside.

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Fire Rescue Superintendent Adam Dewberry told Ben Fordham it took about two hours to get the fire under control.

“The building is pretty unstable and we are concerned of a collapse.”

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Image: TODAY