Firefighters, ambulance staff and police were at the scene of the crash in Edendale, Southland.
A 54 year-old woman was trapped in the car and later extricated.
Police said at 2.40 pm a helicopter was about to airlift her to hospital. She remained in a serious condition.
The crash happened about 1.20pm at a rail crossing on Humphries Rd, police said.
Police were still at the scene, about 33km northeast of Invercargill, and a serious crash investigation was about to begin.
