A federal police officer has told an inquest he believed a knife-wielding teenager would have "cut my throat and cut my head off" if his colleague had not shot the 18-year-old dead in a confrontation outside a Melbourne police station.

Key points: Officer A fired on Haider when he attacked "in a split second"

Officer A fired on Haider when he attacked "in a split second" Officer B feared his throat would be cut, head cut off

Officer B feared his throat would be cut, head cut off Incident happened so fast there was "nothing else we could do"

Numan Haider was killed after attacking a Victoria Police officer and an Australian Federal Police (AFP) officer outside the Endeavour Hills police station in 2014.

Both officers read statements to the inquest describing how the incident unfolded.

In his statement, the AFP officer, known only as Officer B, said he owed his life to the Victorian officer, known as Officer A.

"I'm sure that Haider was going to cut my head off. He was going to cut my throat and cut my head off," Officer B said.

The AFP officer said the pair had arranged to meet with Haider outside the station when the incident occurred.

He told the inquest Officer A had asked Haider to empty his pockets and Haider had asked why.

He said he had been looking inside the car and looked up when he heard a yell and saw Haider had a knife in his right hand.

Officer A said he had just shaken Haider's hand when Haider suddenly attacked him.

"Haider put his hand into his right jacket pocket and pulled out what I saw to be a knife," Officer A said.

"The blade looked to be about six to eight centimetres long, immediately as he pulled this out he lunged towards me."

Officer A told the inquest he blocked the blows with his arm multiple times, and did not at first realise he had been stabbed.

"I have no doubt that he was trying to kill me," he said. "If I had not blocked with my arm he would have hit my ribs and stomach area."

Haider attacked in 'a split second'

The inquest heard the Victorian officer was knocked to the ground and Haider moved on to attack Officer B.

"In a split second he was on me," Officer B told the inquest. "My eye was bleeding and I felt blood running down my face."

Officer B said he did not know he had been stabbed and slashed and could not hear anything while it was happening.

He then heard a gunshot and saw Haider fall to the ground.

"I don't think we could have done anything else at all - there was no time to react."

Officer A said he got to his feet to see the teen crouching over his federal colleague and the Victorian officer told the inquest he had no option but to shoot Haider.

"I started to get to my feet with a mindset that Haider was attempting to seriously injure or kill Officer B," he said.

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"He was attempting to put the knife into Officer B's stomach and stab him."

Officer A told the inquest he fired his gun once, and hit Haider in the head.

"All up it took about 20 seconds for the time I said to Haider that I wanted to search him until I shot him," he said.

"My main thought going through my mind was to stop Haider killing Officer B, my main concern was that I might hit Officer B," he said.

He said if he had not shot Haider, the teen would have killed Officer B and returned to kill him.

"I'm convinced that in the circumstances I had no other option than to shoot Haider," the Victorian officer said.

Federal officer still takes pain medication

Officer B was stabbed in the chest and twice in the shoulder, cutting a muscle in half.

He also sustained liver damage and two facial lacerations and continues to take pain medication for his injuries.

Officer A received two cuts about four centimetres long on his arm, and injury which severed a nerve and required surgery.

Numan Haider had been under surveillance from counter-terrorism police for months. ( Facebook/Fairfax )

Officer A said he still felt weakness and numbness in his hand.

Earlier this week the inquest was told senior police would never have allowed the meeting to happen if all the relevant intelligence was known.

The meeting was authorised because there had been no specific threat to police but it later emerged that Haider had made several threats against police in the lead-up to the meeting.

The inquest has also heard one of Haider's friends, Ljindim Sulejmani, believed he had "snapped" because of pressure from his parents and ASIO.

Police had asked Haider to meet them at the Endeavour Hill police station to discuss his recent behaviour to assess what it meant for national security.

Haider had been under surveillance from counter-terrorism police for several months.

The 18-year-old's passport was cancelled the day before he attacked police.