A head on crash has closed State Highway 1 near Redwood Pass in Marlborough.

Emergency crews were called to the two vehicle crash involving a campervan about 10.40am.

Initial indications suggested there were serious injuries, though the number of people involved has not been confirmed, a police spokesman said.

The Serious Crash Unit has been advised and is expected to examine the scene.

Chris Lynch Media understands the Coastal Pacific train has been stopped before the crash site.

Multiple St John paramedics are at the scene, including rescue helicopters from Nelson, Wellington, and Palmerston North.

The highway remains closed while emergency services work at the site.

An NZTA spokesman said, “The highway is closed to all traffic following a car versus car crash near Cloudy Bay Drive. No local road detours are available.

“The highway is expected to be closed for several hours while the crash is investigated and the scene cleared.

“Drivers must avoid the area until the incident is resolved.

“Those travelling between Marlborough and Canterbury, including those with Picton ferry connections, should detour via the inland route: SH63 Wairau Valley, SH6 Kawatiri Junction to O’Sullivans, SH65 O’Sullivans to Springs Junction, and SH7 Springs Junction to SH1 Waipara.

“This is a significantly longer route and will require extra travel time. Drivers must plan accordingly.

“There is no current estimate for when SH1 will reopen. Updates will be provided when its status changes.”