MetService says the weather on the West Coast is some of the worst they've seen.

Damage to a bridge near Te Taho and a large slip on the Fox Hills are being assessed.

The New Zealand Transport Agency expects some road closures to last for weeks as conditions worsen.

Meteorologist Andy Best says the weather is shocking.

"We've recorded close to 100,000 lightning strikes in the last 24 hours. I don't think we've seen that amount of strikes recorded before."

A state of emergency has been declared in Timaru, with the Rangitata River at risk of bursting its banks. State Highway 1 is shut, and the inland Route 72 - at the upper bridge - is also closed.

RNZ reports SH6 is closed from Hokitika to Makarora, with several slips blocking the road.