Instructors of the People's Liberation Army say it is an exercise that sharpens co-ordination, teamwork and mental strength.

Six soldiers standing in a circle toss a satchel of live explosives between them, counting down until it detonates. Just before it does, the last soldier drops it into a hole and the six men dive for cover.

Any miscalculation would be fatal. The exercise was staged during an exhibition drill in Hong Kong last month, as chief executive, Sir Donald Tsang, inspected the troops.