An early morning fire at Geelong's main mosque was the fifth at a place of worship in the city since last October, with the targeted buildings housing a variety of different religious denominations.

No arrests have been made and police said that while the religious link between the targets was obvious, they had yet to find any evidence that would lead them to a single perpetrator.

The first church fire was lit in the early hours of October 14 last year, at the historic 140-year-old St John the Evangelist Church at Bannockburn, north west of Geelong.

The early morning pattern has continued with each subsequent fire.

October 14, 2015 Bannockburn's 140-year-old St John the Evangelist Church is set alight December 5, 2015

Two churches are set on fire within 30 minutes in Norlane April 15, 2016 Geelong Presbyterian Church in Geelong West is destroyed May 18, 2016 A fire at Geelong's main mosque, which is housed in a former bluestone church

Fire crews were sent to suspicious fires at two churches in the northern Geelong suburb of Norlane on December 5.

They attended the first, at the Baptist Church in Spruhan Avenue, at 4:15am, before receiving calls to another blaze at the St Peter's church on Sparks Road half an hour later.

It was not until April that the next church went up in flames - this time the 103-year-old Presbyterian Church on Geelong West's cosmopolitan Pakington Street.

Again, crews were called to the fire before sunrise at 4:30am.

This most recent incident, at the main point of worship for Geelong's Muslims, could be a case of a mistaken target as they mosque was housed in a former Uniting Church building.

Rumours of links to past history of abuse

Victoria Police believe the fire at the mosque is linked to four previous church fires. ( Supplied: Matthew Richards )

Police said they believed all five fires could be connected, but they had yet to come to any definitive conclusions.

Local Area Commander for Victoria Police in Geelong Inspector Graham Banks said the first four were being treated as a "series", and investigators were keeping an open mind about the mosque fire.

"At this stage we're working on the presumption it may well be connected, but it's certainly not the only avenue of inquiry we're pursuing," he said.

One of two churches targeted by suspected arsonists in the suburb of Norlane. ( Seven News: Estelle Griepink )

There have been rumours that the fires are being lit at churches with links to paedophile priests.

In 2008, John Haines was sentenced to jail for numerous sex offences, some connected to the church at Bannockburn.

Inspector Banks said he did not believe it was a definite link between the targets but was a possibility.

"That's certainly a possibility given that these attacks on churches have occurred when we've got a royal commission examining the behaviour of some people from religious faiths, however it's certainly at the moment it's just an avenue of inquiry that we certainly aren't going to ignore or rule out," he said.

"Until we apprehend the offender, hopefully when we do that person's forthright with his or her reasoning for why they committed the offences."