A Glenroy man arrested as part of an investigation into the supply of weapons to the Brighton siege gunman has been released without charge, after police seized an imitation shotgun during a search of three homes.

Key points: Properties were searched in Glenroy, Ascot Vale and Gladstone Park

Properties were searched in Glenroy, Ascot Vale and Gladstone Park Police said one man arrested, and two being interviewed, could have supplied firearms to the Brighton gunman

Police said one man arrested, and two being interviewed, could have supplied firearms to the Brighton gunman There was no evidence linking the men directly to terrorism, police said

Victoria Police Deputy Commissioner Shane Patton said about 150 officers, from the Special Operations Group and Australian Federal Police (AFP), searched three homes in the northern suburbs of Ascot Vale, Glenroy and Gladstone Park before 5:00am.

He said the raids were related to firearms used by Yacqub Khayre, who shot dead a man, held a woman hostage and wounded three police officers before being shot and killed in Brighton on Monday.

Police said two shotguns belonging to Khayre were found after the siege, including a sawn-off shotgun.

A 32-year-old Glenroy man was arrested during the morning raids but was later released without charge.

Deputy Commissioner Patton had earlier said he sustained "minor grazing to his face" during his arrest.

Deputy Commissioner Patton said a 31-year-old man from Gladstone Park and his 51-year-old father were being interviewed by police, after an imitation shotgun was found at the Gladstone Park address.

"They are not persons of national security interest, but they are persons who are known to us through their criminal history," Deputy Commissioner Patton said.

A talkback radio caller says he saw more than a dozen police searching bins in Ascot Vale. ( ABC News: Peter Lusted )

"As a result of the investigation by the Joint Counter Terrorism Team … it has led us to execute [warrants] this morning.

"They may be involved in the provision of firearms in this matter."

He said police could conduct further raids.

"There's no intelligence of evidence at this stage to suggest that there is any connection between the people we've spoken to this morning, the arrests we've made and terrorism," he said.

"It is an aspect of the investigation that is still ongoing.

"This investigation is very active and there may be further warrants that we'll be executing."

He said police forced entry into a flat in Ascot Vale, which was unoccupied.

Melbourne on high alert

A caller to Fairfax Radio said he had seen more than a dozen police searching bins in a street in Ascot Vale early in the morning.

AFP officers with face masks were seen at several homes in a group of flats at Ascot Vale just before 8:00am.

Four officers could be seen on a balcony, putting items in large plastic bags.

One officer led a sniffer dog around another set of flats.

One witness, who lives in an adjacent set of flats, said he was woken up by the police raid.

"Police just came in and said 'police open up', they got in there themselves," he said.

Melbourne is on heightened alert after the Brighton siege.

Victoria Police has increased police patrols ahead of major sporting events this Queen's Birthday long weekend.

Premier Daniel Andrews is in Hobart for the Council of Australian Governments (COAG) meeting, where he will push to boost counter-terrorism prevention measures.

He has called for a 24-hour specialist Australian Federal Police (AFP) squad based in airports, and changes to the bail system to include intelligence agency and AFP involvement in decisions on applicants with terrorism links.

"What we saw in Brighton was not only deadly, it was evil," he said.

"It is a timely reminder that these threats are not half a world away, they are very real and they are very much part of our daily lives."