US officials say 'likely no survivors' in Potomac mid-air collision

United States officials state that there were likely no survivors after a passenger jet carrying 64 people collided in mid-air with a military helicopter and crashed into the icy waters of Washington's Potomac River.

"We are now at a point where we are switching from a rescue operation to a recovery operation," Washington Fire Chief John Donnelly told a news conference at Reagan National Airport on Thursday.

"At this point, we don't believe there are any survivors," Donnelly said, adding that 28 bodies had been recovered — including one from the helicopter.

As dawn broke over the crash site, emergency vessels with powerful arc lights and inflatables with diving teams could be seen moving back and forth over a wide area of the river.

Donnelly said 300 first responders had been involved in the operation — most of it conducted in pitch darkness.

"These responders found extremely frigid conditions, they found heavy wind, they found ice on the water, and they operated all night in those conditions," he said.

There were no details on the cause of the crash, with transport officials saying both aircraft were on standard flight patterns on a clear night with good visibility.

"Do I think this was preventable? Absolutely," Transportation Secretary Sean Duffy told the news conference.

Dramatic audio from air traffic controllers showed them repeatedly asking the helicopter if it had the passenger jet "in sight", and then just before the crash telling it to "pass behind" the plane.

"I just saw a fireball and it was gone," one air traffic controller was heard telling another after communication with the helicopter was cut.

Meanwhile, the US army unit involved in the overnight collision with a passenger jet near Washington DC has been placed on an operational pause, two US officials reported, meaning helicopters from that unit will not be flying for the time being.

One of the officials, speaking on condition of anonymity, said helicopters from the 12 Aviation Battalion would be temporarily grounded.

It is not clear how long the pause would last.

Other helicopters, like those from the National Guard, will still be allowed to help in recovery efforts, the official added.