Police are appealing for witnesses as they try to track down the southbound car involved in the crash north of Napier on Monday morning.
The crash happened at about 9.30am near Ellis Wallace Road, Eskdale, when two cars collided in wet conditions.
Police said after initial enquiries it appeared that the southbound vehicle may have lost control and crossed the centreline into the path of the northbound vehicle.
One person was out of the wreckage by the time emergency services arrived but the other two occupants were trapped in the wreckage.
After a prolonged rescue operation the scene was finally cleared and the road was re-opened shortly before 12.30pm.
All three injured - a male and two females - aged from 34 to 43, were taken to Hawke's Bay Hospital, 35km away in Hastings.
The occupants of the northbound vehicle received serious injuries. Police said these injuries were not life threatening but were serious.
While the two who had been trapped were initially reported to be in a serious condition, Hawke's Bay District Health Board on Monday night reported their conditions as stable.
Police would like to hear from anybody who may have been following or observed the southbound vehicle - registration number XI8465.
The car is a 1998 green Toyota Prado station wagon.
Anybody with any information that could help, are encouraged to contact Senior Constable Warren Clayton of the Hawke's Bay Police - phone (06) 831 0700.