With a thud that shakes the earth beneath our feet, mud, rock and debris are tipped out of the back hoe of the digger, running down the sides of the gathering pile.
What the excavators hope to unearth are human remains that are evidence of atrocities committed by Japanese military doctors in the years immediately before and during the second world war.
On this plot of land, which still bears the marks of a disused car park, a team of seven men supervised by Kazuhiko Kawauchi began digging the first of six large holes last week. The first excavation revealed the crumbling foundations of a building, which, historians claim, housed the Imperial Japanese Army's medical college where an unknown number of people died in tests designed to reveal the possibilities of chemical, biological or bacteriological weapons.
Set up in 1932 by Major Shiro Ishii in Tokyo's Toyama district, its activities eventually grew so large it was transferred to the northern Chinese city of Harbin and named Unit 731.
Major Ishii and his colleagues then roamed across China for 13 years, carrying out experiments that had been planned and prepared in Harbin, says Jing Chen-min, director of the Unit 731 Museum. They dropped ceramic bombs that contained infected insects from aircraft. They deliberately discarded food contaminated with pathogens fully aware that local people would eat it when they left. Pens and walking sticks were reportedly impregnated with viruses that would then be passed on to anyone who picked them up. They detonated germ bombs and tied naked civilians that they referred to as 'murata' - or 'logs' - to stakes in the sub-zero Manchurian winters and sprayed water on them until they were frozen. Frostbite tests were then conducted to see how much force was required to shatter a limb.
But experiments were still going on in Tokyo right up to the dying days of the conflict and as Japan awaited the arrival of the occupying forces, the officers at the medical college ordered the staff to bury the remains of their victims and remain silent.