LOS ANGELES — Four astronauts from the International Space Station (ISS) have safely returned to Earth a month earlier than planned after one of them developed a serious medical condition.

Their SpaceX capsule splashed down in the Pacific off California, capping a 10-hour-plus descent from the space station and fiery re-entry through Earth's atmosphere.

The team, known as Crew-11, will now receive medical checks before being flown back to land.

It was the first time that NASA has cut short the rotation of an ISS crew due to a health emergency since the station was put into Earth's orbit in 1998.

The Crew Dragon spacecraft dubbed Endeavour parachuted into calm seas off San Diego at about 12:45 a.m. PST (0845 GMT).

In a radio transmission to the SpaceX flight-control center near Los Angeles, Endeavour's commander, NASA astronaut Zena Cardman, 38, was heard saying, "It's good to be home."

Joining her on the return voyage were fellow US astronaut Mike Fincke, 58, Japanese astronaut Kimiya Yui, 55, and Russian cosmonaut Oleg Platonov, 39.

In a news conference after splash-down, Nasa administrator Jared Isaacman said the sick astronaut is "fine right now" and in "good spirits".

Judging by past Nasa communications about astronauts' health, it is unlikely that the identity of the crew member or details of the health issue will be released to the public.

Control of the ISS has been handed over to Russian cosmonaut Sergey Kud-Sverchkov and two other crew members.

The astronauts arrived on the ISS on 1 August expecting to complete a standard six and a half month stay. They were due to come home in mid-February.

But last week, a scheduled spacewalk by Fincke and Cardman was called off at the last minute. Hours later, Nasa revealed a crew member had become ill.

"It's bittersweet," said Fincke when he handed over the keys to the ISS to Kud-Sverchjov on Monday.

In a social media post, he stressed that all crew members on board were "stable, safe, and well cared for".

Orbiting Earth at an altitude of 250 miles, the International Space Station (ISS) makes 16 orbits of our planet a day, travelling at a speed of 17,500 miles per hour.

It is run by five space agencies and carries out wide-ranging scientific research about space and the effects on humans, animals and plants of living in microgravity.

The ISS carries some medical equipment and astronauts are trained to deal with minor medical issues, but it does not have a doctor on board.

The evacuation was a serious test of Nasa's procedures for dealing with medical issues.

By all accounts, it passed, although there may be questions about how well the agency could have responded if the astronaut had suffered a medical emergency.

The early departure leaves the ISS with a skeleton crew of just three astronauts — Nasa's Chris Williams and cosmonauts Kud-Sverchkov and Sergei Mikaev — until another four arrive in February. — Agencies