A total of 20 children and 10 adults were on board the 71-seater coach when a nine-year-old boy fell from the vehicle on the A47 near King's Lynn this afternoon
The youngsters are from Stamford Rugby Club in Lincolnshire and were travelling home after playing in a tournament at Holt in north Norfolk when the incident happened.
Superintendent Dave Marshall said:
A nine-year-old boy is in hospital with "life-threatening injuries" after falling from a coach this afternoon, police have said.Officers in Norfolk said nobody else was injured in the incident, which happened at around 3.45pm on the A47 trunk road near King's Lynn.
A police spokesman said: "The boy has been taken to the Queen Elizabeth Hospital in King's Lynn with life-threatening injuries.
"A number of other people were on board the coach at the time and no other passengers were injured."
The road is expected to remain closed for some time and local diversions have been put in place.Anyone with information is asked to contact police.