An eight-hour armed stand-off at Colac, in Victoria's southwest, has ended with a man dying from self-inflicted injuries, police say.

The siege in a Calvert Street house began at 11pm (AEDT) on Wednesday but four people in the house with the gunman managed to get out at around 3am on Thursday.

A Victoria Police spokeswoman said that around 7.30am on Thursday police heard a gunshot and entered the home to find the man dead.

"It's believed he died as a result of self-inflicted injuries," she told AAP.