At least one soldier is believed to have lost a limb in a collision between troop lorries during an Anglo-Indian exercise on Salisbury Plain.
Up to 20 military personnel were injured in the smash just off a public road across the Plain, with the two most severely injured being flown by helicopter to nearby hospital and another eight classed as seriously hurt.
Police said four or five could have suffered “life-changing” injuries, and military sources said at least one Indian soldier has undergone an amputation.
Both British and Indian troops were badly hurt, but the majority of injured are Indians, the source said.
Exercise Ajaya Warrior was part of a larger war game called Wessex Storm and involved troops from British units including 6 Rifles and a company of Indian soldiers carrying out mock counter insurgency operations in difficult urban terrain. The crash took place at around 6.30pm on Wednesday, in a field near Westdown Camp.
A spokeswoman from South West Ambulance Service said: “From our perspective we have taken two patients with life threatening injuries, and flown them to Southampton.
“One went with Dorset and Somerset Air Ambulance, and the other with Wiltshire Air Ambulance.
“We have taken eight patients with serious injures by road ambulance to Salisbury Hospital.
“We have treated a number of walking wounded – I am saying a number because we don't have a definitive figure.”
She said the rescue operation involved a number of land ambulances, volunteer on-call doctors and two ambulance hazardous area response teams – one from Bristol and another from South Central Ambulance Service.
A number of rapid response vehicles were also involved, as well as two critical care paramedics vehicles.
The gender and ages of the injured people, and the nature of their injuries are not yet known.
A spokesperson for Wiltshire Police said: “We received a call from the air ambulance who told us they were attending.
Initially it was believed 16 people were injured but the number has risen to over 20 and paramedics say some are “critical”.
“First responders and three military ambulances were also at the location, a field on The Plain near Westdown Camp.
“It happened on a by-way which cuts through The Plain.
“It is still regarded as a Wiltshire Police matter as it's on a by-way, although it's off the main road.”
It is not yet known which hospitals the injured soldiers were taken to for treatment.
A spokesman for the Ministry of Defence said: “We are aware of an incident in the training area of Salisbury Plain. We are not absolutely certain of the details and until we are, we will not be making any comment.”
The Royal School of Artillery is based at Larkhill and provides training in the use of artillery equipment, including both technical and tactical training.
A post on the Indian Army's Facebook page prior to the incident said the two armies were currently carrying out a joint exercise called Ajeya Warrior to “enhance their ability to undertake joint tactical level operations in (a) counter insurgency/counter terrorism environment”.
Salisbury Plain, a 300-square-mile area of land, which includes the prehistoric stone circle at Stonehenge, is owned by the Ministry of Defence and is Britain's biggest military training area.