A plane carrying 71 people from Bangladesh swerved erratically and flew dangerously low before crashing and erupting in flames as it landed Monday in Kathmandu, Nepal's capital, killing at least 50 people, officials and witnesses said.

A top airport official said the pilot of US-Bangla Airlines flight BS211 did not follow landing instructions from the control tower and approached the airport's one runway from the wrong direction.

"The airplane was not properly aligned with the runway. The tower repeatedly asked if the pilot was OK and the reply was 'yes,'" said Raj Kumar Chetri, the airport's general manager.

But a recording of the conversations between the pilot and air traffic controllers indicated confusion over which direction the plane should land.

In the recording, posted by the air traffic monitoring website liveatc.net, conversation veers repeatedly about whether the pilot should land on the airport's single runway from the south or the north.

Just before landing the pilot asks "Are we cleared to land?"

Moments later, the controller comes back on, using a tone rarely heard in such conversations — perhaps even panic — and tells the pilot: "I say again, turn!"

Seconds later, the controller orders firetrucks onto the runway.

The exact number of dead and injured remained unclear amid the chaos of the crash and the rush of badly injured people to nearby hospitals, but Brig. Gen. Gokul Bhandari, the Nepal army spokesman, said it was clear that at least 50 people had died. Officials at Kathmandu Medical College, the closest hospital to the airport, said they were treating 16 survivors.

US-Bangla Airlines flight BS211 from Dhaka to Kathmandu was carrying 67 passengers and four crew members, according to an airline spokesman.