Up to 17 vehicles are stuck in snow on the Crown Range in Otago tonight, police say.

Heavy snow has resulted in in two campervans and a further 10 to 15 vehicles stick on the Crown Range - Cardrona Valley Rd.

The council and roading contractors had been advised, and Police units with four-wheel-drive vehicles were on their way to help, police said in a statement.

Motorists were being advised to take extra care on roads in parts of the South Island tonight.

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In Westland, a tree had come down on Haast Pass Highway and another fallen on Whataroa Highway at Harihari, between Main Rd.

In Canterbury, police said a tree had reportedly fallen on power lines on Homebush Rd, Coalgate.

"All drivers are being urged to drive to the conditions and report any road blockages to police."

Metservice has also issued heavy rain warnings Westland and the Tararua Ranges as wet weather moves in early Sunday morning.

The Tararua Ranges were expected to accumulate between 90 - 120ml overnight and into Sunday morning and 60 - 90ml about Westland, meteorologist Josh Griffin said.

"It could possibly lead to localised flooding, maybe even some landslips," he said.

The rain was heading north up the country and was expected to ease off from about 9am in the south but not until early Monday morning for the Tararuas, north of Wellington.

A heavy rain watch was also in place for the Kapiti Coast from late Sunday morning to Sunday night.