Two people were airlifted to Boston-area hospitals and two others taken to local hospitals after a Thursday afternoon accident in Plaistow, N.H., involving four vehicles. They found four vehicles involved in, what was described as, “a serious motor vehicle accident.” Two of the vehicles were overturned and several people had to be removed. Police withheld for the time being the names drivers and passengers of the vehicles while an investigation continues. They said all were treated by emergency medical services and advanced life support teams from both the Plaistow and Haverhill Fire Departments. Plaistow Police is leading the investigation with assistance from the New Hampshire State Police Collision Analysis and Reconstruction unit.