UPDATED 9.06PM: It's been a rough day for rural fire crews in the South Island and things could get worse yet.

Police are warning a vegetation fire burning out of control near Oxford, northwest of Christchurch, could get worse, as winds are forecast to pick up further.

A number of houses have been evacuated, with police going door-to-door telling other residents they need to be prepared to go at a moment's notice.

Senior Sergeant Roy Appley said the winds are continuing to push the fire around.

"Over the next four hours it's meant to get stronger rather than die down, so that's going to keep things more difficult than they otherwise could be.

An evacuation centre has been set up at Oxford Area School.

Meanwhile, a separate blaze on farmland in South Canterbury has closed State Highway One and the main trunk line on the South Island's east coast.

Fire is lining both sides of the road in the Bankside area, north of the Rakaia Bridge, and fire service communications shift manager Riwai Grace said crews are preparing to work into the night.

"It's quite a large fire with resources attacking it from all sides."

Grace said several homes have been evacuated already and its unclear whether they'll be more come. 

Drivers are asked to follow the direction of Transport Agency contractors and be ready to drive on unsealed roads.

Further south, a welfare centre's been opened for Mosgiel residents displaced by fires that have blazed there today.

Both fires were fanned by hot, strong winds throughout the day and houses were damaged.

Otago rural fire officer Jaime Cowan said the blazes are under control now, but the extent of damage to houses is not yet known.

All residents can now use water as normal, after Dunedin City Council earlier urged water conservation after power was cut to water pumps.

The council will keep a water tanker at the intersection of Braeside and Clyde Street until tomorrow as a precaution.