Firebug blamed for 25 fires across Melb

An arsonist is being blamed for at least 25 fires in Melbourne's northern suburbs over the past seven weeks.

Six of the fires were started on Wednesday night over a 40-minute period, with fire crews rushing to douse the blazes in Dallas, West Meadows and Broadmeadows.

Other fires were deliberately lit in bush and grassland near Lara Douglas Reserve in Dallas between December 1 and January 1.

A male riding a pushbike was seen near a number of the fires and investigators believe he may be able to assist them with their inquiries.

Detective Senior Sergeant Michael Gaul said it was fortunate all fires were quickly contained and called on members of the public to come forward with information.

"With a strong wind, these fires could pose a major threat to the Dallas residents," he said on Thursday.

"Even the smallest, seemingly insignificant detail could be vital to solving this case."