New Hampshire State Police investigate the crash Friday on Interstate 95 in Greenland, N.H. The bus was carrying 11 children participating in a Kittery recreation program.

Children aboard a van headed from Kittery to a New Hampshire water park Friday morning were injured when the driver suffered a medical emergency and the vehicle crashed off Interstate 95 southbound in Greenland, New Hampshire, authorities said. One of two adult counselors in the vehicle also was reported injured.

One of the 11 children on board the van 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. The children range in age from 7 to 10, officials said.

Hennessy said he could not discuss the nature of the medical emergency suffered by the 21-year-old driver. He said the nature of that emergency and other elements of the crash are under investigation.

The driver, a seasonal employee of the town of Kittery, and one child were taken to a hospital in Portsmouth, New Hampshire, for injuries that were initially considered serious, said Hennessy, but those injuries were not as bad as officials first 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 people, and authorities provided no new information Friday night.

Citing police, NECN, the New England cable TV network, identified the driver as John Guy of Kittery.

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

“It appears the vehicle drove off the roadway into the woodline and struck a large tree, causing significant damage to the front end,” NECN quoted Hennessy as saying. “Most of the children did have seat belts on.”

Two buses were also taking children from Kittery to the water park. They were ahead of the van that crashed and continued on to Candia, their drivers apparently unaware of the crash, Hennessy said.

Kittery Town Manager Kendra Amaral said the van that crashed is owned by the town and the two buses are owned and operated by a contractor.

Amaral said that none of the injuries from the accident were considered life-threatening.

Police said the most seriously injured were the driver, an 18-year-old counselor and a 10-year-old student, The Associated Press reported.

“We contacted all of the parents of the children on the van,” Amaral said in an email. “They were reunited with their children at the treating hospitals. Once we contacted all of the impacted families, we began reaching out to the families of the other children on the other buses.”

She said town officials contacted the parents of the children on the van and helped to make arrangements for parents to pick up the children at the New Hampshire hospitals where they were taken.

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

Amaral said the trip to the water park was part of the town’s SAFE program. SAFE is primarily an afterschool program and is currently operating a nine-week summer program, she said.

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 van from the trees and towed it from the scene.

Staff Writer Matt Byrne contributed to this report.