Firefighters have warned of the "drain" on their resources after they spent more than two hours tackling a blaze in a derelict mill.
Crews were called to the Pagefield building in Swinley at 2.10pm on Wednesday after rubbish was deliberately set alight in a small annex building.
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Three fire engines were needed and crews wore breathing apparatus while fighting the fire.
They remained there until 4.30pm, as the location of the fire and condition of the building made it difficult to tackle.
Mike Fairhurst, crew manager at Wigan fire station, said: "It's a drain on our resources. We could be doing better things than fighting our way around a dangerous, derelict building. The buildings aren't in a good state of repair, they are very dangerous."
The former mill and college building has previously been a hot-spot for arson attacks and anti-social behaviour, but measures had been taken to secure it.