NASA astronauts Suni Williams and Butch Wilmore's return to Earth will be further delayed until at least late March, the agency said, taking what should have been an eight-day stay on the International Space Station to more than nine months.

A new crew is needed to go to the space station before Mr Wilmore and Ms Williams can make their return journey. They can leave only after the “handover period”, which allows lessons to be shared with the newly arrived crew for “a better transition for ongoing science and maintenance at the complex”, is over, Nasa said on Tuesday.