Sixty-seven people are believed to have died after a passenger plane hit a military helicopter in mid-air near Washington DC's Ronald Reagan airport on Wednesday evening.

National Transportation Safety Board Chairwoman Jennifer Hommendy described the investigation into the crash Wednesday night as an “all-hands-on-deck event” for the agency during a news conference Thursday in which she appeared with members of the board and a senior investigator overseeing the probe.

Sixty-seven people are presumed dead after a passenger plane on approach to Reagan National Airport near Washington, DC, collided Wednesday night with a US Army helicopter midair, sending both aircraft into the Potomac River below,