The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea from 4pm Thursday (May 8) to 1am Friday (May 9).

An active front preceded by heavy rain and gale northwesterlies is expected to move northwards over the South Island during Thursday and Friday morning.

Expect 100 to 150 mm of rain near the main divide and 60 to 90 mm within 15km east of the divide. Peak rates of 15 to 25 mm/h expected about the divide with possible thunderstorms.

Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Anyone heading into Mt Aspiring National Park is advised to take extra care or delay travel.