The horse was destroyed at the scene.
The motorcycle was carrying a pillion passenger when it collided with the wandering horse about 9.30pm near the intersection of Golf Links Road, Whakatane.
Another vehicle was seen to swerve to avoid the horse immediately prior to the crash and police want to speak to the occupants or driver of this vehicle as witnesses for the crash investigation. The vehicle was travelling north toward Matata.
The 21-year-old male motorcycle rider is currently in Waikato hospital in a serious condition and his 16-year-old female pillion passenger is currently in Tauranga Hospital with moderate injuries.
The police serious crash unit is investigating the crash.
The occupants of the vehicle being sought, and any other witnesses, are asked to contact Whakatane police on 07 308 5255.