Maryborough Police Sergeant Michael Wentworth said the incident happened just before 1am in Princes Park, Maryborough.

Sgt Wentworth said a group of youths in the park were approached by a male and female with a pram.

There was an altercation between the two groups after which the male with the female produced a knife.

The man slashed the victim's face leaving a gash from under his chin up to his left ear.

"The assailant is unidentified at this stage and we don't have much to go on," Sgt Wentworth said. "We have a brief description and they had a pram with them."

Sgt Wentworth said it was not confirmed if there was a baby in the pram at the time of the attack.

Ambulance Victoria spokesman John Mullen said a specialist medical team from Melbourne treated the victim who had lost a lot of blood.

"The Adult Retrieval team from the Royal Melbourne Hospital was flown up to prep and stabilise the man at the scene," Mr Mullen said.

The man was then taken to Maryborough Hospital for further treatment before being flown to Melbourne.

He arrived at Royal Melbourne Hospital about 3.30am in a critical condition and was expected to undergo extensive surgery.