The child and a 33-year-old man died at the Cunninghams Road in Tyaak property, after fire engulfed the house about 11.40pm on Saturday.

A 34-year-old man was taken to hospital where he remains critical, police said on Sunday.

Police believe 13 people were staying at the holiday property for the long weekend and a number of people were taken to hospital with injuries.

Three adults went to hospital in a serious condition and one was in a stable condition, Ambulance Victoria said.

Four children were also taken to hospital with serious conditions.

It is understood some other people were assessed at the scene.

Seymour Sergeant Daniel Raynor says the Arson and Explosives Squad is investigating the cause of the deadly blaze.

"Detectives are still speaking to those family members (in hospital) to try to ascertain the exact occurrences," he told reporters in Tyaak.

"Obviously given the extremely tragic circumstances and the situation that we now have, those conversations and those investigations, I dare say, will be ongoing for some time."

Firefighters took an hour and a half to bring the blaze under control.

Australian Associated Press