SALEM, N.H. — Twenty-one people were injured Thursday morning when a school bus, a pickup truck and a dump truck collided at Lake Street and North Broadway, according to police.

Seventeen children were transported to Lawrence General Hospital while four adults were sent to Holy Family Hospital in Methuen, according to Salem Fire Battalion Chief Craig Lemire, the incident commander. He described their injuries as minor, consisting of bumps and bruises for the most part.

They were taken to hospitals as a precaution, Lemire explained.

While the accident is still being investigated by Salem and state police, Deputy police Chief Joel Dolan said it appears to have been a chain reaction collision.

The accident was reported at 10:11 a.m. Children from a summer camp program and staffers were on a field trip to a bowling alley, according to a press release from Little Sprouts, a network of preschools that is based in Lawrence.

Transporting 21 people to hospitals was a massive operation, with the Salem Fire Department requiring assistance from several neighboring communities plus Lawrence General Hospital. Four Salem ambulances were joined by two each from Derry, Londonderry and Lawrence General; and one each from Hampstead, Methuen and Windham.

The dispatchers were effective in enlisting the additional ambulances, Lemire said.

"They know who to call," he said. The accident scene was under control by 11:38 a.m., according to Lemire. The Fire Department cleared the scene by 12:31 p.m. while police remained there investigating, he said.

Awaiting the victims were the emergency medical teams at Lawrence General and Holy Family hospitals.

"We're always prepared for this," said Jill McDonald Halsey, chief marketing and communication officer for Lawrence General. "We're prepared for the unexpected."

Lawrence General, she pointed out, dealt with a much larger crisis when the gas explosions and fires of Sept. 13 sent numerous people to hospitals.

“The safety and wellness of every child in our care is always our greatest priority. I’m very proud of how our team collaborated with local authorities to put the children’s needs first. Now, our primary focus is to surround the children, families and staff who were involved in today’s accident with love,” Sarah Schroeder, chief executive officer of Little Sprouts, said in a statement to the media.