House explosion 2

The explosion knocked bricks off a large chunk of the front of the house at 1335 Hamilton Road. (Gary Ennett/CBC News)

London police are calling an explosion and fire that sent one person to hospital and caused significant structural damage to an east-end London home "suspicious." 

Police made the announcement Thursday, three days after fire officials began sifting through the blast site inside a one-storey home at 1335 Hamilton Road in the city's east-end. 

The explosion rocked the Hamilton Road and Clarke Road neighbourhood when it happened on Monday afternoon, with reports that it could be heard up to a kilometre away.

The blast sent one man to hospital with second degree burns to hands, face and back. He's still in hospital with serious injuries. Three other people inside the building at the time managed to escape without injury. 

Police say the owner of the home was away at the time the explosion, though there has been no word on a cause of the detonation.

The London Police street crime unit has now joined investigators with the Ontario Fire Marshall and the London Fire Department in what has now become a criminal investigation.