Home Minister Radzi Sheikh Ahmad said about 600,000 illegal immigrants faced detention, deportation and jail sentences. He advised them to leave before the Muslim Eid-ul-Fitr holiday at the end of this month.

"They should find their own way to return home, including using legitimate exits," Radzi was quoted as saying by the state Bernama news agency.

If they are lucky, they may get away. If not, they will be detained for violating immigration regulations," he said.

Malaysia conducts periodic sweeps for illegal immigrants, mainly Indonesians who work in the country's plantation and construction sectors.

Radzi said RELA, a uniformed civilian task force which participates in campaigns to track down and detain illegal immigrants, was already rounding up people.

"In fact, RELA is detaining some 80 illegal immigrants a day," he said.

Since 1992, Malaysia has launched several operations against illegal workers, but each one has led to a labour shortage followed by a new wave of illegal immigration -- a pattern which was apparent after a blitz last year.

Malaysia is one of the largest importers of foreign labour in Asia. Foreign workers, both legal and illegal, number around 2.6 million of its 10.5 million workforce, officials say.