Attack shows 'extreme acts' possible: PM

Prime Minister Tony Abbott says the stabbing of police officers in Melbourne showed some Australians were capable of "extreme acts".

An 18-year-old shot dead by police in Melbourne on Tuesday night was a known terrorism suspect.

The Narre Warren man stabbed an Australian Federal Police officer and a Victorian policeman outside the Endeavour Hills police station on the city's outskirts before being shot.

Mr Abbott, who is in Hawaii on his way to a United Nations meeting in New York, said the Melbourne man had mounted a "fierce attack" on the police officers.

"Obviously this indicates that there are people in our community who are capable of very extreme acts," he said.

"It also indicates that police will be constantly vigilant to protect us from people who would do us harm."

Mr Abbott said he had spoken to the wives of the police officers to assure them of the government's support and respect for the professionalism of their husbands.