A last-minute problem nixed Saturday’s launch attempt for Boeing’s first astronaut flight, the latest in a string of delays over the years.

Two Nasa astronauts were strapped into the company’s Starliner capsule when the countdown was automatically halted at 3 minutes and 50 seconds by the computer system that controls the final minutes before lift off.

With only a split second to take off, there was no time to work on the latest issue and everything was called off. It was not immediately clear why the computers aborted the countdown.

Launch controllers were evaluating the data, said United Launch Alliance’s Dillon Rice. But it is possible the team could try again as soon as Sunday.

Astronauts Butch Wilmore and Suni Williams remained in their capsule seats, as they waited for technicians to help them get out.

The first launch attempt on May 6 was delayed for leak checks and rocket repairs.

Nasa wants a backup to SpaceX, which has been flying its astronauts for four years. (AP)