One person was med-flighted to a Boston hospital Thursday afternoon with critical injuries following a two-car accident on Meshacket Road in Edgartown.

Five people were taken to the Martha’s Vineyard Hospital with injuries following the crash. Four were treated and released, and a fifth was med-flighted, a hospital spokesman confirmed.

The crash involving a black Audi and a Tisbury Taxi took place around 5 p.m., just as the Edgartown Fourth of July parade was getting underway, and took place during what police and fire officials said was one of the busiest Fourth of July holidays in recent memory.

Edgartown police chief Antone Bettencourt said that prior to the accident, the black Audi sedan was traveling toward the Edgartown-West Tisbury Road and Morning Glory Farm. In the area of the old landfill, he said, the Audi passed Oak Bluffs police chief Erik Blake, who was in an unmarked vehicle. The Audi was traveling at “a high rate of speed,” Chief Bettencourt said, estimated at 60 miles per hour.

Fourth of July holiday was busiest in recent memory for emergency calls, Edgartown police said. — Alison L. Mead

Chief Blake then witnessed the Audi side swipe a Hummer going in the other direction, Chief Bettencourt said.

As the Audi turned around a corner it collided head-on with a Tisbury Taxi going in the other direction, he said.

Three people were in the Audi, assistant fire chief Alex Schaeffer said, two in the front and one in the backseat. The passenger in the backseat was unrestrained and had a severe head injury, he said.

The taxi had one passenger, Chief Schaeffer said, and both people in the taxi had minor injuries. All five people were transported to the Martha’s Vineyard Hospital, and the person with the severe head injury, listed in critical condition, was med-flighted off the Island. The police did not yet have the names of the people involved in the accident.

Chief Bettencourt said the accident is still under investigation, but the driver of the Audi , a man, will be summonsed and charged with negligent operation and speeding. There is also an investigation into whether the driver was impaired due to alcohol, he said.

Traffic backed up on Meshacket Road following two-car crash. — Alison L. Mead

Chief Bettencourt said that for both police and the fire department, this was “one of the busiest Fourth of Julys I can remember as far as calls for service during the actual events of the parade and the fireworks.”

“It was quite a busy day yesterday,” Chief Schaeffer agreed. There were 11 different medical calls from 3 p.m. to 1:30 a.m., he said, and out of those 11 calls, 24 patients were treated.

“Pretty hefty numbers for one town,” he said.

Edgartown had two additional ambulances on loan through mutual aid from Oak Bluffs, and all four ambulances responded to the Meshacket accident, he said. During that time, a Tri-Town ambulance responded to an allergic reaction outside the Dukes County jail because the Edgartown ambulances were busy.

“Without the help from Oak Bluffs and Tri-Town we wouldn’t have been able to handle [the volume],” Chief Schaeffer said.

Just after 6 p.m., police responded to a three-car motor vehicle accident near the Triangle on Edgartown-Vineyard Haven Road, just outside the entrance to Your Market. A Nissan truck allegedly turned in front of a blue Jeep traveling outbound, the police report said, causing the Jeep to collide with an Audi waiting to exit the Your Market entrance. The driver of the truck, William Bassett, 66, of Edgartown, was arrested on a drunken driving charge.

At 9:14 p.m, while the fireworks were underway over the Edgartown Harbor, Chief Bettencourt said an assault took place on North Summer street. After an argument over a parking spot, a 27-year-old man allegedly reached into a car and assaulted the driver and the passenger, who sustained injuries to their faces. Chief Bettencourt said the man, Mark Joaquin of Dartmouth, allegedly took off running and a Chilmark police officer observing him began a foot chase. Mr. Juaquin was caught outside the Seafood Shanty, Chief Bettencourt said, and will be summonsed on two counts of assault and battery.

Chief Bettencourt credited careful preparation for the ability to respond to the calls, noting that there was mutual aid with other towns. The marine patrol boat had two medical assists on the harbor, he said. “Every person that we had out there . . . . everybody was pretty much tapped with calls.”