It took New Bedford firefighters about 20 minutes to put out a fire in a vacant house at 40 Liberty Street Tuesday afternoon.

District Fire Chief Michael Dandurand says that the back porch was completely destroyed and the back wall of the house was heavily damaged with the fire spreading and damaging the aluminum siding on the house next door.

The fire caused about $20,000 in damage and it remains under investigation although officials say it appears the fire started outside the building, as all of the windows were boarded up and the utilities were shut off. No firefighters were injured battling the blaze.