CHICHESTER -- A 3-year-old boy and his 26-year-old female caretaker, both of Barnstead, were seriously injured in a crash that closed Route 4 for more than three hours Monday, state police said.

The names of the victims have not been released, but police reportedly said the woman is not the boy’s mother.

Both victims were taken to Dartmouth-Hitchcock Medical Center. It took about an hour to extricate the woman, and she was taken to the hospital by medical helicopter, police said.

The crash happened about 12:45 p.m. near the intersection of King Road. The woman’s car was traveling eastbound when it struck the side of an oncoming tractor-trailer truck carrying propane that was going westbound, police said.

“For reasons under investigation, the operator of the sedan crossed the center lane and struck the tanker truck in the rear portion” of the truck, said Lt. Mark Armaganian of New Hampshire State Police Troop D.

The driver of the truck, a 57-year-old man from Durham, Maine, was not injured.

The truck belongs to Propane Transport International. Due to the damage to the tractor-trailer, workers had to offload fuel from one PTI truck to another on the side of the road.

Armaganian said “there is no breach of hazardous materials” from the accident.

Route 4 is a major east-west thoroughfare between Interstate 93 in Concord and the Epsom Traffic Circle. The speed limit where the crash occurred is 50 mph, but police said they’re investigating how fast the vehicles involved were traveling.

The accident scene is about the same spot where State Rep. Sally Kelly, D-Chichester, was seriously injured in a head-on crash in October 2009.