A woman who went swimming in Japan has been rescued after being swept 80km (50 miles) away from the beach she was on with her friend.

The Chinese national in her 20s, who was wearing a rubber ring, spent 36 hours in the water before being spotted by a cargo ship off a peninsula south of Tokyo.

A smaller vessel nearby was alerted and two of its crew jumped into the sea to rescue her, the AFP news agency reports.

Coast Guard helicopters then took the woman, who was dehydrated but conscious, to hospital, according to the Kyodo news agency.

Police were alerted on Monday evening when the woman, who has not been named, was reported missing after going swimming in Shizuoka Prefecture to the south-west of the capital.

“It was around 7:55pm [10:55 GMT] on July 8 when we received the information after the woman’s friend reported to a nearby convenience store that she was missing,” a local Japan Coast Guard official told AFP.

He said there was “80km in a straight line” between the beach she was on and the place where she was rescued off Chiba prefecture’s Boso peninsula.

“But it is assumed she drifted for an even greater distance.”

The woman told rescuers that she had been unable to return to the beach after being swept out to sea because of the rubber ring.