One person has died in a Waikato crash which injured three others.

A helicopter was called to the two-car collision on Paeroa-Tahuna Road, about 10 minutes southwest of Paeroa.

Emergency services were called to the Otway area not long before 5pm on Thursday.

One person died at the scene, says police and Fire and Emergency.

Firefighters were working to free others from their vehicles, says fire northern communications shift manager Colin Underdown.

One patient, initially in a serious condition, was downgraded to moderate but was flown to Waikato Hospital, says a St John spokeswoman.

Two other patients in moderate condition were taken to Thames Hospital.

The Serious Crash Unit is investigating the crash.