Bricks dating back 5,000 to 7,000 years have been unearthed in northwest China's Shaanxi Province, adding between 1,000 to 2,000 years onto Chinese brick-making history, archaeologists claimed Saturday.

"The five calcined bricks were unearthed from a site of the Yangshao Culture Period dating 5,000 to 7,000 years ago. Previously, the oldest known bricks in the country were more than 4,000 years old," Shaanxi Provincial Institute of Archaeology researcher Yang Yachang said.

The bricks, including three red ones and two gray ones, all uncompleted, Yang said. The site under excavation is located at Liaoyuan Village of Baqiao District, and Huaxu Town, Lantian County of Xi'an, capital of Shaanxi Province.

Yangshao Culture is a Neolithic culture that flourished along the Yellow River, which runs across China from west to east. The culture was named after Yangshao, the name of the first village discovered of the culture, in 1921 in central China's Henan Province.

Archaeologists used to believe the ceramics were applied to architecture in the Shang Dynasty (1600 B.C-1100 B.C.), which had been proved wrong by the new discovery, Yang said.

The smooth surface and rough surface of most well preserved red bricks are vertical to each other, and the rough surface was designed to be stuck to other materials, Yang said.

"It is still unknown whether the bricks were in a square or rectangle shape as none of them are complete," he said.

The site, called Lantian New Street Site and covering an area of more than 200,000 square meters, was to be cut through by a new highway, said Shao Jing, assistant researcher of the institute.

The salvage excavation was launched in August 2009. As of February, more than 2,300 square meters had been excavated, Shao said.

More than 150 sites, including houses, ash pits, ash grooves and kilns, had been found in the area, Shao said.

"The bricks were all discovered in ash pits, which were garbage containers for the ancient people. For the modern archaeologist, these garbage containers are treasure troves of artifacts," she said.

The world's oldest unearthed bricks date back 8,000 to 10,000 years. They were discovered in Middle East and they were adobes which had not been calcined. Thus, the brick-making history of human kind should be about 10,000 years, Yang Yachang said.