XI'AN: About two tons of ancient coins were accidentally discovered on the grounds of a primary school in Liquan county of Shaanxi province - a significant discovery for the research of China's ancient coins, official said.

"The coins were found by accident on Tuesday when the school's playground was under construction," Zhao Aiguo, director of the county heritage and tourism bureau, told China Daily on Friday.

Preliminary research and identification showed that the coins were made and used in the dynasties of Tang (618-907), Song (960-1127) and Yuan (1271-1368), Zhao said.

Workers reported the discovery to the local heritage authority and police.

Archaeological experts and police rushed to the site and the construction was stopped for rescue excavation, Zhao said.

Archaeologists found that the coins were in a 1.5 sq m, 1 m high pit made with blue bricks underground.

The site was part of the ruins of Xiangjici Temple, which was built by Emperor Liu Heng (202 - 157 BC), the fifth emperor of Western Han Dynasty (206 BC - 24 AD), as a memorial for his mother Queen Bo, Zhao said.

The original temple had a tower and some houses, which were all destroyed. An historic tower that still stands next to the school was built in 834 in the Tang Dynasty, Zhao said.

The place where the coins were kept might have been underground storage for keeping the money donated by people who visited the temple, Zhao said.