Tragedy struck on Thursday when two individuals working on power lines near the Mississippi River lost their lives after their helicopter collided with the lines, hitting a barge and igniting a fire that released thick black smoke, according to officials.

The helicopter, operating near East Alton approximately 20 miles (32 kilometers) north of St. Louis, crashed into the barge on Missouri’s side of the river. Authorities confirmed no additional injuries occurred.

Adam Briggs was on the opposite shore when it all happened and filmed the crash scene.

“The helicopter was conducting maintenance work on the power lines when it struck one, detonated, and burst into flames,” described an eyewitness in a video as flames flared amid the billowing smoke. “A pilot and a technician were onboard; the helicopter exploded and descended onto the barge where it’s currently in flames.”

“They’re dead. They have to be dead,” said Briggs in shock.

A representative from the power company Ameren mentioned that a contractor alongside a subcontractor had been engaged in the repair and replacement of tower lighting and marker balls on the lines.

“Our thoughts and sincere sympathies are with the victims’ families and coworkers,” Ameren expressed in a statement, noting their commitment to cooperating fully with the investigation.

Following the collision, approximately a dozen agencies from Illinois and Missouri responded swiftly, stated Kyle Gaines, spokesperson for the St. Charles County Ambulance District.

The nearby fire department rushed by boat to the crash site and a private tug boat helped to douse the flames, said Alton Deputy Fire Chief Matt Fischer.

No one was on the barge when the helicopter smashed into it and the fire has been extinguished, the state patrol said. The river has been closed to commercial traffic.

The helicopter crashed around 11 a.m. Thursday on the Mississippi River about half a mile (800 meters) downriver from the Melvin Price Lock and Dam, said Rivers Pointe Fire District Chief Rick Pender.

Pender said federal agencies were on the way. The FAA and National Transportation Safety Board will investigate the crash. The NTSB said an investigator was expected to arrive on site Friday. The helicopter, the agency said, was an MD 369, which are typically smaller.

In 2018, a helicopter crew stringing new powerlines crashed in Pennsylvania, killing two people and injuring the pilot.

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Associated Press reporters Jack Dura in Bismarck, North Dakota; Beatrice Dupuy in New York City; and Rio Yamat in Las Vegas contributed.