One person is in critical condition after a two-vehicle crash south of the Bombay Hills early this morning.

Fire Service had to free one person from one of the vehicles and two from the other vehicle after the crash on the Waikato Expressway between Pokeno and Mercer about 5am this morning.

A St John Ambulance spokeswoman said St John took at least one person to Middlemore Hospital in critical condition and one person in serious condition.

The spokeswoman was unsure of the condition of the other persons involved in the crash.