The driver, a 42-year-old female ambulance technician, and the patient, an 88-year-old man, were pronounced dead at the scene.
A male crew member and a male relative of the patient remain in hospital both in a serious condition.
Police are continuing to appeal for witnesses following a collision involving an ambulance and a car in the New Forest.
A driver arrested in connection with the incident on the A337 yesterday morning has been bailed until July 29.
The 25-year-old, who was driving a blue Seat Alhambra, was arrested on suspicion of causing death by driving without due care and attention.
Both the car and the ambulance were heading north on Lyndhurst Road when, for reasons yet to be established, the ambulance came off the road and hit a tree.
A motorist remains in police custody after an ambulance driver and an elderly patient were killed when an ambulance crashed into a tree in Hampshire.
The car involved in the incident, a blue Seat Alhambra, was also travelling north, according to police. The 25-year-old male driver, from Brockenhurst, was uninjured.
Inspector Kirsty Shannon, of Hampshire Police, said:
This is a very tragic incident and our sympathies are with the families of the ambulance driver and patient.
Clearly, we are in the early stages of our investigation and are examining the events prior to the collision. Contrary to rumours circulating, however, there is no suggestion any wildlife was involved.
I would urge anyone who witnessed the collision or saw either vehicle prior to it to contact us.
Hampshire Police have asked for witnesses to come forward after an ambulance driver and an elderly patient were killed when the ambulance hit a tree in Hampshire.
Any witnesses to the collision on A337 this morning are asked to contact our Road Death Investigation team on 101 ref: Operation Feldberg
Our thoughts are with the families of the ambulance driver and the patient who died in the collision in the New Forest this morning.
Paul Jefferies, area Manager at the South Central Ambulance Service has said it is a "sad day", after a paramedic and an elderly patient were killed when an ambulance hit a tree in Hampshire.
Mr Jefferies added that the service would continue to work with Hampshire Police to help their investigation:
A motorist has been arrested after a paramedic and an elderly patient were killed when an ambulance crashed into a tree. In a statement South Central Ambulance Service said:
A double crewed ambulance belonging to South Central Ambulance Service NHS Foundation Trust (SCAS) was involved in a collision with a tree on the A337 Brockenhurst to Lyndhurst road at 09.35 this morning.
A female member of the ambulance crew and the elderly male patient were pronounced dead at scene.
A male relative of the deceased patient was collared and boarded at scene and has been conveyed to Southampton General Hospital by land ambulance.
Two other cars were involved in the incident apart from ambulance.
Police will not give further details at this stage and will not identify the people involved for at least 24 hours.
Gwyn Williams was over taken by the ambulance shortly before the crash and told ITV news what he saw:
He had been driving along the A336 between Brockenhurst and Lyndhurst in the New Forrest.