Heavy snow could fall in eastern parts of the South Island overnight.

MetService says rain has become persistent in Otago and South Canterbury tonight, and should spread to North Canterbury and Kaikoura Sunday morning.

Initially snow is expected down to about 600 metres, falling to 300 as temperatures cool tomorrow.

Significant snow is expected to 400 metres in the foothills of Canterbury between the Waitaki and Rakaia Rivers from early tomorrow morning.

Above 500 metres, up to 30 centimetres could accumulate in the hills of eastern Otago, the Canterbury foothills south of the Waitaki River, and north of the Rakaia, as well as Banks Peninsula and the Kaikoura Ranges.