Fire crews will fight any blazes in Christchurch “aggressively” as dry conditions lead to an increased number of fires in the Port Hills.

Twenty properties near Cass Bay were evacuated on Tuesday as three helicopters with monsoon buckets battled a fire that burned through 15 hectares of scrub in the hills above. The cause of the fire has not yet been determined.

The fire was contained by 5.30pm and residents were able to return home.

The blaze was one of several in Canterbury on Tuesday as strong winds of up to 130kmh fanned flames, lifted roofs, and damaged trees.

Fire and Emergency New Zealand (Fenz) assistant area commander Mike Bowden said scrub growth and dry conditions had compounded the problem on the Port Hills, which had already had “several reasonable-scale fires” this summer.

A fire caused by fireworks on December 11 burned through 25 to 30ha of scrub on the city side of the hills. A few days, later a spark from construction work caused another fire nearby, which spread across about 16ha of grass and gorse.

MetService said strong winds were also forecast on Wednesday, but would start to die out on Thursday. Temperatures are expected to reach the low 20s for the rest of the week, before highs increase to the mid 20s at the weekend.

The Port Hills were a “significant risk” to Christchurch and firefighters would attack any future fires “aggressively”, Bowden said.

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