BEIJING (AFP) - Two grave robbers trapped underground in a Chinese Tang dynasty tomb for more than 24 hours were rescued by police, who promptly arrested them, state media said on Monday.

The pair were among five suspected thieves in the northern province of Shaanxi who were excavating a grave which was among a cluster of emperors' mausoleums and tombs dating from the Tang Dynasty (618-907 AD).

Two of them became stuck in a chamber 20m underground, the official Xinhua news agency said, adding they feared the structure could collapse or they could suffocate from a lack of oxygen.

It quoted police officer Sun Weidong as saying rescuers pulled them out through a crack at the top of the chamber. All five suspects were detained, it added.

Tomb raiding occurs with some regularity in China, whose ancient civilisation has left a wealth of relics buried underground. Police investigated 451 tomb-raiding cases in 2010, state media said.