HARBIN - Incineration pits and traces of explosives left by Japanese invaders destroying evidence have been found at the remains of Japan's notorious Unit 731 headquarters in Harbin, capital of Northeast China's Heilongjiang Province, researchers said on Thursday.

The new findings were part of an operation to destroy a bacteria lab and burn experimental facilities at the site, according to researchers with the Heilongjiang Provincial Institute of Cultural Relics and Archaeology.

They directly suggest the Japanese army attempted to destroy evidence of crimes before retreat, said Li Chenqi, a researcher with the institute.

More than 1,000 relics were excavated from the site of Unit 731 over the past two years, the provincial culture department said. Mainly metal and glass vessels and ceramics, the relics were unearthed after workers excavated an area of 15,337 square meters at the site, including a bacteria lab and prison used to house people for biological experiments, the department said.

Unit 731 was a top-secret biological and chemical warfare research base established in Harbin in 1935 as the center of Japan's biological warfare in China and Southeast Asia during WWII. The retreating Japanese invaders blew up the base when the Soviet Union took Harbin in 1945.