One person has died after a car crashed off a bridge into the Moeraki River north of Haast.

Emergency services are at the scene at the Moeraki River Bridge on Haast Highway this evening.

A police spokesperson said emergency services were called at 6.49pm about the incident.

"Three people got out of the vehicle safely, while one remained trapped," the spokesperson said.

"The road is closed and motorists are asked to please avoid the area."

It is believed the car crashed off the road and into the river. It appeared to be about three to four metres below the surface of the water. The weather conditions in the Haast area were said to be fine.

St John spokesman Gerard Campbell said a helicopter from Greymouth had arrived at the scene around 8.30pm.

The Serious Crash Unit has been notified of the incident.