Six helicopters, a plane and seven fire crews are battling a large vegetation fire in the South Island's Waitaki District.

Fire and Emergency (FENZ) was alerted to the out-of-control burnoff near Tokarahi at around midday on Friday.

Strong winds fanned the blaze overnight. It has so far burned through approximately 400 hectares of farmland, tussock and scrub.

FENZ incident controller Bobby Lamont said the fire was not contained or controlled.

Lamont said much of the fire-ground was not easily accessible for vehicles, and they were having to airlift firefighters in.

"Winds are forecast to gust up to 100km/h here today. We anticipate we'll be at this fire for some days."

A command unit has been set up near the fire-ground.

Lamont said it was very dry in the Waitaki valley and Central Otago, and so they were asking anyone considering lighting an outdoor fire to check the weather and wind forecast before they proceed.

Strong winds had been forecast for the region by MetService.