Melbourne Bishop Philip Huggins said he had told Imam Mohammad Ramzan he could use the hall of All Saints church in Newtown for Friday prayers, if needed.

Bishop Huggins said the church wanted to help "our Muslim friends continue their devotional life".

The roof and interior of the Geelong mosque - a bluestone former church - were destroyed by the fire in the early hours of Wednesday morning.

Residents were woken about 2am by a bang so loud that some thought it was thunder or an explosion.

When the residents ran outside, they found an enormous blaze consuming the building on Bostock Avenue.

"They [the neighbours] ran and got hoses but saw it was so big that these hoses weren't going to do anything," 3AW's Pat Mitchell told Fairfax from the scene.

"Given the size of the fire, it's amazing surrounding buildings including their houses were actually able to be saved."

Seven fire trucks eventually put the blaze out, but by then the entire centre of the structure had been turned to ash.

The original bluestone walls were still standing.

As well as the mosque, four churches in Geelong have been consumed by suspicious blazes since October last year.

• The Geelong West Presbyterian Church burnt down in a suspicious fire on April 15 this year.
• Two churches in Norlane, a suburb north of Geelong, burnt down after arson attacks on December 6, 2015.
• St John The Evangelist church in Bannockburn was gutted by fire early on the morning of October 15 2015 – although this blaze wasn't treated as suspicious at the time.

On Wednesday morning police said it is believed those four blazes were connected.

"This [the mosque fire] is one of a series of fires against places of worship in this area," Geelong inspector Geelong's Inspector Graham Banks said.

"There's been five since September last year ... We believe those fires are connected."

Inspector Banks believes the mosque may have been targeted because someone mistook its bluestone facade for a church, rather than a mosque.

"It is clearly not what people might envisage a mosque might look like," he said.

"Certainly if you drove past it the vast majority of people would not know if it was a mosque."

Bishop Huggins, whose episcopal area includes Geelong, wrote to the Islamic Council of Victoria offering the church hall, through Father Peter Martin, the Vicar of St James and St John in Queenscliff.

The bishop said there were close ties between Father Martin and Imam Ramzan.

"We appreciate how shocking and distressing the destruction of a place of prayer and community strengthening  is," Bishop Huggins said.

He said the church would look to help in others ways.

He said it wanted to show support for the Muslim community in the context of media coverage which he said could leave some Muslims feeling isolated.

"I think it is important to reach out to convey our support and friendship during distressing times, which is why we did what we did this morning," Bishop Huggins said.

The mosque, in the north-western Geelong suburb of Manifold Heights, is actually a refurbished Uniting Church.

The building was sold to the local Muslim community more than 20 years ago

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