Officials and witnesses said that the plane had struggled to become airborne, then smashed into a maintenance building at the airport after pilots circled back to land.
Commissioner James Rovella of the Department of Emergency Service and Public Protection said 13 people, including three crew members, were aboard the plane at the time of the crash.
The death toll of seven could rise, according to Rovella. Hours after the crash, he also indicated that some of the victims had been burned, and were “very difficult to identify”.
The airport confirmed in a tweet that a Collings Foundation Second World War aircraft was involved in an accident.
In a statement, the Federal Aviation Administration (FAA) said the vintage Boeing B-17 aircraft crashed at the end of Runway 6 while it was attempting to land just after 10 a.m.
Fire and black smoke rose from the airport as emergency crews responded to the crash.
Authorities said that some of the survivors were critically injured, as well as a firefighter and one person on the ground at the time of the crash.
Connecticut state police, along with the FBI and FAA and Homeland Security are now investigating the crash.
“Officials have closed Bradley International airport, and the FAA has put in a ground stop for flights that are destined for the airport,” the FAA statement reads.
Antonio Arreguin told the Associated Press he had parked at a construction site near the airport for breakfast when he heard an explosion. He said he did not see the plane but could feel the heat from the fire, which was about 250 yards away.
“In front of me, I see this big ball of orange fire, and I knew something happened,” he said. “The ball of fire was very big.”
WATCH: Video shows aftermath of airplane crash in Connecticut
A smaller explosion followed about a minute after the first blast, he said. He saw emergency crews scrambling within seconds.
According to the FAA, the aircraft is civilian-registered and is not flown by the military.
The aircraft is one of five vintage fighter planes on display at the airport as part of a travelling exhibit honouring Second World War veterans.
In a tweet Wednesday, Conn., Gov. Ned Lamont said his “prayers are with everyone who was on board.”
“Such an unfortunate situation with an historic aircraft,” he wrote.
In a tweet posted Wednesday afternoon, Sen. Richard Blumenthal called for an immediate National Transportation Safety Board investigation.
“Our hearts go out to the loved ones of the victims,” he wrote, “they & the public deserve to know the facts & cause of this tragic crash.”
The NTSB has since sent a team of 10 to investigate the cause of the crash.
– With files from The Associated Press