Senior Sergeant Dave Byrt, of Footscray police, said the 15-year-old boy and several friends were attacked by a group of about 40 people in front of Maribyrnong Aquatic Centre about 4.15pm.

It is believed weapons, including knives, umbrellas and a hockey stick, were used during the altercation.

The victim was chased to the underground car park of Highpoint, where he collapsed with stab wounds to the chest.

The youths fled when police arrived.

The boy was taken to the Royal Melbourne Hospital in a stable condition. He is assisting police with their inquiries.

Senior Sergeant Byrt said there were about 200 people aged 13-20 in the area, but police were unsure how many were involved.

Police have spoken to about 50 people but have made no arrests and the investigation is ongoing.

Senior Sergeant Byrt said such incidents did not occur regularly, though there had been problems with groups of young people at the shopping centre in the past.

He said Highpoint had sufficient security and its management liaised with police and offered a room for them to operate from the shopping centre.

Samantha Taranto, spokeswoman for GPT, which runs Highpoint, said the shopping centre would help police with the investigation.

"Our security noticed it happening and called the police.

"They acted as crowd control to ensure the safety of our customers."