A 21-year-old New Hampshire woman remained in a Boston hospital with life-threatening injuries yesterday following a two-car crash on Barnes Road that marred Fourth of July festivities on the Vineyard Wednesday afternoon.

The crash left five people injured, three of them seriously, state police said.

The three people were later flown by medical helicopter to Boston hospitals, including Heather LaFlamme, 21, of Berlin, N.H., who was reported in critical condition at Brigham and Women’s Hospital in Boston Thursday afternoon.

A preliminary investigation by state troopers from the Oak Bluffs state police barracks found that a red 2012 Jeep Wrangler with four occupants from New Hampshire and a black 2009 Volkswagen Tiguan driven by a 19-year-old Cambridge man collided near the entrance to the Airport Mobil station just after 2 p.m. Wednesday.

The Jeep, traveling southbound on Barnes Road, apparently pulled to the right side of the road and then turned to the left to make a U-turn. The Volkswagen, which was traveling behind the Jeep, came up on the left side of the Jeep, broadsiding it during the U-turn, state police said. The collision caused the Jeep to roll over and the Tiguan to veer off the road.

Ms. LaFlamme was ejected from the Jeep’s back seat, state police said.

The Jeep’s other back seat passenger, Seth Jones, 26, of Dummer, N.H., was flown to Boston and admitted to Beth Israel Hospital with serious injuries. The Jeep’s front seat passenger, Margaret Jones, 51, of Dummer, N.H., was also flown to Boston and admitted to Beth Israel with serious injuries.

The driver of the Jeep, Thomas C. Jones, 51, was transported to the Martha’s Vineyard Hospital with serious injuries, state police said. The driver of the Tiguan, Benjamin T. Johnson, 19, was released after being taken to the Martha’s Vineyard hospital for evaluation.

Barnes Road was closed off while police, ambulance, fire and emergency medical technicians responded to the scene. Traffic snarls ensued among hundreds of cars that were making their way to Edgartown for the annual Fourth of July parade on a warm, sunny day that had begun with rain but saw blue skies by afternoon. Barnes Road remained closed at both ends from the blinker light intersection to West Tisbury Road, for more than five hours. The town of Edgartown sent out an automated text alert asking drivers to avoid the area as they drove into Edgartown for the 5 p.m. parade. The road was reopened to all traffic just after 7 p.m.

State police said an investigation is continuing to determine if criminal charges are warranted. Troopers are looking into whether the speed of the Tiguan was a contributing factor, and whether the right-side placement of the Jeep’s steering wheel affected the driver’s vision while taking the U-turn, police said.

The state police collision analysis and reconstruction team were transported to the Island by the state police Air Wing on Wednesday. Investigators are interviewing witnesses and examining evidence to determine the sequence of events and potential causes of the accident, state police said, and no determinations have been made.

Troopers from the Oak Bluffs state police barracks and the Edgartown police are being assisted in the investigation by troopers from the state police crime scene services and the Cape and Islands detective unit.