A team of Cambodian and Japanese archaeologists said it has uncovered an ancient man-made drainage system at the site of the Bayon temple at Angkor Thom, local media reported on Thursday.

The temple, built in the late 12th and early 13th centuries during the reign of King Jayavarman VII, has been the subject of three digs since 1999, but this is the first time such a drainage system has been discovered, according to the archaeologists.

"The drainage system is for rainwater flow from the first and second levels," the Phnom Penh Post quoted Heng Kamsan, one of the archaeologists as saying.

Heng Kamsan said 14 metres of the 70-centimetre-wide drain had been dug up, and that its covering of laterite stone was due to be removed next week.

He said the archaeologists had at first been hoping to learn more about the condition and construction of the temple's foundation.

After one largely fruitless month of work, however, he said the archaeologists were elated to happen upon the drainage system.

"While we did not expect to find it, we did, and it has made us happy," he said.

The ongoing dig, which began in January, is being carried out under the auspices of UNESCO and the Apsara Authority, which manages the Angkor Wat temple complex. The dig was expected to conclude by the end of March, according to Heng Kamsan.