The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea from 10am-7pm Monday (December 15).

An active front, preceded by strong moist northerlies, moves across the South Island on Monday, followed by showery westerlies.

Between 120 to 160mm of rain is expected about the main divide, and 70 to 100mm within 20km farther east.

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.