Lake Illawarra Police are appealing for information as investigations continue into a violent home invasion at Flinders overnight.

About 3.40am on Sunday, emergency services were called to a home on Mummuga Close, Flinders, following reports of a home invasion.

Lake Illawarra Police District officers attended and were told four unknown males wearing balaclavas, one armed with a knife, forced entry into the home's converted garage and assaulted a 20-year-old man.

Three other occupants – two men aged 19 and 43, and a 37-year-old woman – attempted to assist, but the residents were also assaulted by the group of intruders, who then ran away from the scene.

NSW Ambulance paramedics treated the 43-year-old man for stab wounds to the head and chest, the 20-year-old man for a stab wound to the leg and stomach, and the 19-year-old man for significant facial injuries.

They were taken to hospital in a serious condition.

A crime scene has been established and investigations are continuing.

Anyone with information is urged to contact Lake Illawarra Police District or Crime Stoppers on 1800 333 000.