One person is dead and two others have been injured in a horrific stabbing at a mosque at Dallas, in Melbourne's northern suburbs.

Police say a group of elderly men and women were meeting at the Broadmeadows Turkish Islamic Cultural Centre when a 22-year-old man tried to get inside.

Detective Senior Sergeant Stuart Bailey says the young man was in an agitated state.

"Three people in that mosque tried to prevent him from entering. They are all in their 70s," he said.

"The male has produced a knife and has stabbed all three of them."

When a police sergeant arrived on the scene he was assaulted by the man.

"Fortunately for police the critical incident response team (CIRT) were also nearby and attended. They deployed capsicum spray which didn't stop the offender," Detective Senior Sergeant Bailey said.

The man then ran off into the mosque carpark where he was tasered.

It took six of the CIRT members and two uniform police officers to finally subdue the man.

A Glenroy man in his 70s was killed in the attack and two others were injured. Both are in a stable condition.

The suspect was also taken to hospital.

Police say the man had been at the mosque the previous day.

Detective Senior Sergeant Bailey says there were a large number of witnesses and police are trying find out what prompted the attack.

"It's an horrific attack on three elderly gentlemen just trying to go about their normal business at the mosque," he said.