About 550 Vietnamese were this morning being given two hours' notice to pack and leave Whitehead detention centre before hundreds of officers in riot gear go in to remove them.
The group was to be flown back to Vietnam on five deportation flights scheduled to depart this month.
Section Four of the camp, targeted for today's operation, was all quiet yesterday except for some inmates being spotted making weapons.
A search of the camp on Monday turned up about 1,500 weapons including spears, daggers and missiles.
Today's exercise was to be the first major operation since almost 100 Vietnamese escaped from Whitehead in May during a riot which broke out in the hours before a removal operation.
Millions of dollars' damage was sustained and negotiations are continuing over compensation for prison officers whose cars were destroyed by fire.
Efforts to clear several sections of Whitehead have been stepped up to make way for the 6,000 boat people on Tai A Chau who will be moved to the camp in September.