SINGAPORE: A Singapore Airlines (SIA) flight bound for Singapore returned to San Francisco almost nine hours after departure because of an "unruly" passenger, the national carrier said on Thursday (Oct 15).

The passenger on board flight SQ31 "became unruly and injured himself in the process", an SIA spokesperson said.

The pilots assessed the situation and decided to turn the aircraft back to San Francisco.

The flight had departed San Francisco at 11.51am local time on Wednesday (2.51am on Thursday, Singapore time). It landed uneventfully at San Francisco International Airport at 8.41pm local time, eight hours and 50 minutes after departure.

The passenger was then handed over to local authorities, SIA said.

The delayed flight departed again for Singapore at 11.18pm local time with a new set of crew members.

A Reddit user who said he was on the flight described it as the "craziest" experience he had encountered.

According to his account, about three hours after takeoff, a passenger began screaming and kicking seats and attempted to reach an emergency exit.

The passenger continued yelling and kicking even after being restrained, the Reddit user said, adding that he was later arrested.

SIA did not provide details about what the passenger did on board or the nature of his injuries.

"We thank our customers and crew members who assisted in managing the situation on board the flight," the SIA spokesperson said.

"SIA sincerely apologises to all affected customers for the inconvenience caused. We are providing all necessary assistance, including rebooking of connecting flights."

The airline said the safety of its customers and staff was its top priority and that it was working closely with the relevant authorities.