The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea from 2pm Wednesday June 25 to 6am Thursday June 26.

An active front, preceded by north to northwest gales, is forecast to move across the South Island from Wednesday through to Friday this week.

Expect 150 to 200 mm of rain near the main divide and 100 to 150 mm within 20km east of the divide. Peak rates of 15 to 25 mm/h expected about the divide.

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.