"Multiple" people are injured after two separate bus crashes on a South Island highway.

Police said the single-vehicle crashes occurred 100 metres apart on State Highway 8 - the Tekapo-Twizel Highway - about 8.40am on Thursday.

"There are multiple injuries, the extent of which is still being confirmed."

About 40 firefighters from four crews around Twizel, Lake Tekapo, Omarama and Otematata are at the scene.

Hato Hone St John said it was notified of the incidents at 8.38am and multiple units are responding to the scene.

The road is closed between Tekapo and the intersection with State Highway 30.

The New Zealand Transport Agency currently has a black ice and winter driving conditions warning out for that stretch of road.

Three helicopters are attending the accident scene.