Children aboard a bus heading from Kittery on a summer field trip were injured when the driver suffered a medical emergency and the bus crashed off Interstate 95 southbound in New Hampshire Friday morning.

One of the 11 children onboard the bus was transferred to a hospital in Boston with serious injuries, said Lt. John Hennessy of the New Hampshire State Police.

He said other injuries were not considered serious.

Hennessy said he could not discuss the nature of the medical emergency suffered by the 21-year-old driver, whom he declined to identify. He said the crash is under investigation by police.

The driver and one child were taken to a hospital in Portsmouth, New Hampshire, for injuries that were initially considered serious, said Hennessey, but turned out to be not as bad as officials feared. The other children were taken to a hospital in Exeter, New Hampshire. One of those children had serious injuries that necessitated the transfer to a hospital in Boston, Hennessy said. He didn’t have updated conditions on the injured.

The children were part of a summer program operated by the Kittery Recreation Department. Henesssy said they were on a field trip to a water park in Candia, New Hampshire.

Two other buses were also taking children from Kittery to the water park. They continued on to Candia, apparently unaware of the crash, Hennessy said.

Parents went to the Exeter hospital to pick up their children early Friday afternoon.

In an emailed statement, Kittery Town Manager Kendra Amaral said that none of the injuries from the accident were considered life-threatending. She could not be reached for further comment.

Repeated calls to the Kittery Recreation Department were not returned Friday.

The bus is registered to the Recreation Department in Kittery, New Hampshire officials said.

Amaral’s statement said the bus was on a SAFE program field trip. SAFE is an afterschool program, which is currently operating a nine-week summer program.

The statement said all the parents of the children on the bus have been contacted by town authorities.

The crash happened on I-95 southbound in Greenland around mile marker 10.6. Police closed several lanes of traffic, but reopened most by 11:15 a.m. By early afternoon, a wrecker had pulled the bus from the trees and towed it from the scene.