He said the threatened officer backed away into a stairwell. The cornered officer then fired on the boy as did two others as they tried to defend their colleague. Assistant Commissioner Cartwright said the police officers had done everything they could before opening fire on the youth.

"I don't think the police were trigger happy but that's why we have the coroner," he said. "The members have reacted as we would want them ... they've ultimately had no choice." He said it was not known how many shots were fired and the incident was over in a matter of two to three minutes.

The teenager is believed to have stolen two knives from a nearby Kmart after threatening staff. Assistant Commissioner Cartwright said the youth had earlier tried to take kitchen knives from his home but his family had disarmed him.

He said there was no suggestion the boy suffered from mental illness or was drug-affected at the time. It was not known what had triggered his rage. "The family's rightly very, very upset," he said. Police were called to the Northcote Plaza Shopping Centre car park about 9.20pm yesterday after receiving up to four calls from the public about an agitated male carrying knives.

Assistant Commissioner Cartwright said the officers - two female constables, a leading senior constable and a senior constable - had tried to calm the armed teenager who ran a short distance to the skate park before approaching one of the police officers and threatening to kill them. Seconds after a warning shot was fired into the ground, three of the officers shot at the youth who was standing up to 14 metres away.

"This is a dreadful tragedy,'' Assistant Commissioner Cartwright said. He defended the actions of the officers and said they had been trained to fire at the central body mass rather than shoot to wound. "The movies would portray that you can shoot to disarm people. That's not our experience. These are events that are life-threatening. People are extremely nervous, agitated, scared."

Assistant Commissioner Cartwright said he could not say if the use of stun guns would have saved the teenager's life and Victoria Police had not ruled out deploying the weapons in the future. The lives of the teen's family and the officers had been changed forever by the shooting, he said.

The Homicide Squad and coroner are investigating the death. Assistant Commissioner Cartwright said the coroner would look at whether the teen had wanted police to kill him. Search and rescue unit officers were this morning using metal detectors to scour the skate park. The boy's body has reportedly been removed.

Plain-clothes police officers were this morning canvassing members of the public for information, while a broad cordon surrounding the park had been tightened. At a separate press conference last night, Assistant Commissioner Cartwright described the incident as a "dreadful tragedy".

"Our condolences are certainly with the family," he said, adding that the police officers were "pretty shaken". "We shouldn't lose members of the community this way,'' he said. "We train our police members. They've foamed him [with capsicum foam], they talked to him and they've done what they can [before he was shot]. It's a dreadful event." Resident George Markopoulos said he heard five or six shots fired within a few seconds.

"I knew straight away they were gunshots," he said. "I've been living here all my life and it's the first time anything like this has happened." Another resident, Wally Taleb, described it as "scary, shocking and not something you see every day".

Police have requested surveillance footage from inside the Kmart store, which is believed to show the boy slashing boxes in an agitated state. This morning a woman, who appeared to be aged in her 50s, laid flowers at the site where the boy died. Police escorted a man and woman, consoling each other, to the park.

Three young men, who appeared to be in their late teens and who were also comforting each other, arrived at the skate park with a bouquet of flowers and placed them on the skate ramp. They silently surveyed the area where the teenager was shot.