Chinese archaeologists said underground passages in the ruins of an ancient Chinese capital near Xi'an might have been dug during complex power struggles in the Han Dynasty 2,200 years ago.

"The underground passages are the first ever discovered in the ruins of an ancient Chinese capital," said Liu Qingzhu, a researcher with the Chinese Institute of Archaeology in the Chinese Academy of Social Sciences (CASS).

"The tunnels were mostly discovered under the palaces where the royal women lived, including the emperor's mother, the empress and the emperor's concubines," Liu said.

Historical records show the emperors in the Western Han Dynasty (206 BC - 25 AD) relied partly on the families of the imperial females to consolidate their rule.