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The mine fire blanketing the Victorian town of Morwell in thick smoke is suspicious, police say.

The blaze, which is burning inside the Hazelwood open-cut coal mine, has been active for more than a fortnight and is expected to remain so for at least another two weeks.

Police say they are concerned an arsonist may be at work in the area.

They say the fire began on the Strzelecki Highway between Morwell and Mirboo North about 1.30pm (AEDT) on February 9.

It progressed through a timber plantation, causing significant damage to plantings, fences and structures, before making its way into the mine.

JUST IN: #CFA confirms extra tankers have been deployed to the #Morwell coal fire following a flare up. #9News pic.twitter.com/J1yNIac0G8

— Nine News Melbourne (@9newsmelb) February 25, 2014

An arson chemist has attended the scene and police are treating the fire as suspicious, they said in a statement on Tuesday.

They say there were also several smaller suspicious grass fires in nearby Yinnar, Hazelwood and Boolarra on January 28 and again on the morning of February 9.

Investigators believe the arsonist could continue to light fires on high danger days and want to speak to anyone who noticed suspicious behaviour in the area.

Fire Services Commissioner Craig Lapsley said he expects the mine fire will burn for another two weeks.

“The last 12 days we’ve been able to get over 50 per cent of the fire out,” he told ABC Radio on Tuesday.

“Based on that if we continue the same progress that takes us to the 14 days.”