RIYADH (AFP) - The Saudi authorities began on Monday a clampdown on illegal immigrants after the end of an amnesty that gave overstayers and workers a grace period to leave or legalise their status.

Police patrols will be searching for illegally staying foreigners and those who help them, Interior Ministry spokesman General Mansur al-Turki said late on Sunday.

Violators will be arrested, penalised and deported, he said.

Nearly a million Bangladeshis, Filipinos, Indians, Nepalis, Pakistanis and Yemenis, among others, have taken advantage of the three-month amnesty - announced on April 3 and then extended for four months - and left the country.

Another roughly four million have legalised their situation by finding employers to sponsor them, a must to reside in most Gulf monarchies.

Foreigners desperate to work in the country were willing to pay for sponsorship, and sponsoring expatriates has become a lucrative business for some Saudis.

But under the new rules, workers can be employed only by their own sponsors, banning the practice of working independently or for non-sponsors.

Thirty Filipino workers who returned home on Monday alleged they were abused in the process of leaving.

"They treated us like animals," said domestic helper Amor Roxas, 46, alleging that police placed them in crowded cells before they were taken to the airport.

"Our feet were chained," said Ms Yvonne Montefeo, 32.

Saudi Arabia, the world's largest oil exporter, is seen as a gold mine for millions of people from Asia and elsewhere in the Arab world, who find work as common labourers, drivers, porters and house maids.

Expatriates account for around nine million of the country's 27-million population.

Saudi Arabia has the Arab world's largest economy, but the unemployment rate among natives is above 12.5 per cent, a figure the government is aiming to reduce.