Doorway believed to be the entrance of the Bandidos on the Dunns Cresent industrial estate in Dandenong.

The Bandidos' clubhouse in Dandenong. Photo: Michael Clayton-Jones

The owners of factories surrounding an outlaw motorcycle gang's Dandenong clubhouse are being refused insurance cover after the property was firebombed and shot up in separate incidents.

Insurer CHU Underwriting Agencies has told the business owners in the industrial estate that it will not renew the insurance policy - which covers common property and public liability - when it expires on August 25 because of the Bandidos.

Factory owners at the 22 Dunn Crescent estate were advised of the decision after a bomb exploded outside the clubhouse's steel-armoured front door on July 25.

Earlier in the month, the clubhouse was shot at by someone armed with an AK-47.

The Bandidos and the Hells Angels have been engaged in a simmering feud since the shooting of Bandidos enforcer Toby Mitchell at a Melton industrial estate in March.

Arson and explosives squad Detective Sergeant Lionel Joseph said the explosion had been large enough to smash windows of neighbouring properties.

Owners' corporation manager James Parnell, of Binks & Associates, said the cancellation of the insurance policy meant 80 other businesses located on the premises, including manufacturers and mechanics, could be unable to sell their properties and face multimillion-dollar exposure.

Buildings in the complex are insured for a total of almost $20 million, and several are listed for sale. ''Banks might call in their loans, and there are all those terrible things that go with having no insurance on a mortgaged property,'' Mr Parnell said.

Compounded by tough economic times, Mr Parnell said, some businesses may have to close. It is understood two are on the verge of closure.

Last week, the owners' corporation wrote to the clubhouse owner, believed to be a Bandidos member, requesting that the club vacate the premises, but Mr Parnell has received no reply.

The letter indicates the owners' corporation did not know the Bandidos occupied the site before the bombing and shooting, and Mr Parnell said club members ''generally kept to themselves''.

The attacks on the Bandidos' Dandenong clubhouse are part of a spate of shootings and firebombings at bikie headquarters across Melbourne.

The AK-47 attack is believed to have been revenge for an assault on the Hells Angels' new ''Darkside'' Seaford chapter, which was shot up in June.

Other business owners in the estate were reluctant to speak about their neighbours.

''We are playing with dangerous people so you have to be careful,'' one said.

Another said he would expect the owners' corporation to take responsibility to find another insurer, and expected the Bandidos would not welcome the news.

''It will be interesting to hear what the Bandidos say. I would guess they'll tell the body corporate to get f-----,'' the owner said. ''I didn't even know they were there, to be honest, until the bombing.''