WINDSOR LOCKS, Conn. — A World War II-era B-17 bomber with 13 people aboard crashed and burned Wednesday at New England’s second-busiest airport after encountering mechanical trouble on takeoff. A state official said at least seven were killed.

The four-engine, propeller-driven B-17G Flying Fortress struggled to get into the air and slammed into a maintenance shed at Bradley International Airport as the pilots circled back for a landing, officials and witnesses said.

In this aerial image taken from video, emergency crews respond to the crash of a B-17 Flying Fortress at Bradley International Airport in Connecticut Wednesday. (WFXT Boston 25 News via AP)
In this aerial image taken from video, emergency crews respond to the crash of a B-17 Flying Fortress at Bradley International Airport in Connecticut Wednesday. (WFXT Boston 25 News via AP)

The restored heavy bomber had 10 passengers and three crew members, authorities said. The state official who gave the death toll was not authorized to discuss the investigation and spoke on condition of anonymity.

Black smoke rose from the airport as emergency crews responded to the crash at the airport in Windsor Locks, Connecticut, just north of Hartford.

In this photo provided by Antonio Arreguin, smoke fills the sky after a B-17G Flying Fortress crashed Wednesday outside Bradley International Airport north of Hartford, Conn. (Antonio Arreguin via AP)
In this photo provided by Antonio Arreguin, smoke fills the sky after a B-17G Flying Fortress crashed Wednesday outside Bradley International Airport north of Hartford, Conn. (Antonio Arreguin via AP)

Connecticut Public Safety Commissioner James Rovella said hours after the crash that some of those on board were severely burned, and “the victims are very difficult to identify.”

At least six people were taken to the hospital, three of them critically injured, authorities said. One person on the ground was also hurt.

“Right now my heart really goes out to the families who are waiting,” Gov. Ned Lamont said. “And we are going to give them the best information we can as soon as we can in an honest way.”

The retired, civilian-registered plane was associated with the Collings Foundation of Stow, Massachusetts, which brought its “Wings of Freedom” vintage aircraft display, two World War II fighter planes and three bombers, to Bradley International this week.

The vintage bomber, one of the most celebrated allied planes of World War II, was used to take history buffs and aircraft enthusiasts on short flights, during which they could get up and walk around the loud and windy interior.

This Collins Foundation B-17G Flying Fortress, pictured in Tampa, Florida, was in Connecticut this week for an aircraft display. It crashed at about 10 a.m. (Howard Altman/Staff)
This Collins Foundation B-17G Flying Fortress, pictured in Tampa, Florida, was in Connecticut this week for an aircraft display. It crashed at about 10 a.m. (Howard Altman/Staff)

The Flying Fortress was a few minutes into the flight when the pilots reported a problem and said it was not gaining altitude, officials said. They lost control when the plane touched down and it struck the shed just before 10 a.m.

The airport was closed afterward but reopened a single runway about 3½ hours later.

Flight records from FlightAware show the plane had traveled about 8 miles and reached an altitude of 800 feet.

In recordings of audio transmissions, a pilot told an air traffic controller that he needed to return to the airport and land immediately. Asked why, he said: “Number four engine, we’d like to return and blow it out.”

The National Transportation Safety Board sent a team to investigate the cause of the crash.

Brian Hamer, of Norton, Massachusetts, said he was less than a mile away when he saw a B-17, “which you don’t normally see,” fly directly overhead, apparently trying without success to gain altitude.

One of the engines began to sputter, and smoke came out the back, Hamer said. The plane made a wide turn and headed back toward the airport, he said.

“Then we heard all the rumbling and the thunder, and all the smoke comes up, and we kind of figured it wasn’t good,” Hamer said.

Antonio Arreguin said 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.”

A smaller explosion followed about a minute after the first blast, he said. He saw emergency crews scrambling within seconds.

“Our thoughts and prayers are with those who were on that flight, and we will be forever grateful to the heroic efforts of the first responders at Bradley,” the Collins Foundation said in a statement.

A view from an earlier flight of the restored Boeing B-17G Flying Fortress heavy bomber -- over the Tampa, Florida, area in February --that crashed Wednesday. (Howard Altman/Staff)
A view from an earlier flight of the restored Boeing B-17G Flying Fortress heavy bomber -- over the Tampa, Florida, area in February --that crashed Wednesday. (Howard Altman/Staff)

“The Collings Foundation flight team is fully cooperating with officials to determine the cause of the crash of the B-17 Flying Fortress and will comment further when details become known."

The same plane also crashed in 1987 at an air show near Pittsburgh, injuring several people, the foundation said. Hit by a severe crosswind as it touched down, the bomber overshot a runway and plunged down a hill. It was later repaired.

The crash reduces to nine the number of B-17s actively flying, said Rob Bardua, spokesman for the National Museum of the U.S. Air Force, near Dayton, Ohio.

Boeing-built B-17 Flying Fortresses — 74 feet long, with a wingspan of 104 feet — were used in daylight bombing raids against Germany during the war. The missions were extremely risky, with high casualty rates, but helped break the Nazis’ industrial war machine.

The B-17 that went down was built in 1945, too late to see combat in the war, according to the Collings Foundation.

It served in a rescue squadron and a military air transport service before being subjected to the effects of three nuclear explosions during testing, the foundation said. It was later sold as scrap and eventually was restored. The foundation bought it in 1986.

“This is kind of shocking. It’s a loss to lose a B-17,” said Hamer, whose father served in the Air Force. “I mean, there aren’t very many of those left.”

Collins reported from Hartford. Associated Press writers Michael Melia and Susan Haigh contributed to this report from Hartford.

Chris Ehrmann is a corps member for Report for America, a nonprofit organization that supports local news coverage, in a partnership with The Associated Press for Connecticut. The AP is solely responsible for all content.