An unidentified Nigerian man has died in a Japanese immigration detention centre, bringing to an end a hunger strike an activist group said was intended to protest his being held for more than three years.

The man in his 40s, died on Monday after he fainted and was rushed to a hospital.

The cause of his death was unknown at the time of filing this report.

RINK, a group supporting detainees at the centre, told Reuters that the Nigerian had been on hunger strike to protest his lengthy detention.

Another 27 foreigners are on hunger strike at a detention center in Ushiku, northeast of Tokyo, said a separate group supporting detainees at that facility.

Some of them have gone without food for 47 days, said Kimiko Tanaka, a spokeswoman for the group.

But the Japanese authorities said they were providing medical care for the detainees and trying to persuade them to eat.

Japan held about 1,500 detainees as of June 2018, according to the latest public data, nearly half of them for more than six months.

Some 604 were asylum seekers whose applications were rejected, while the rest were held for various immigration infractions such as overstaying visas.