After a tortuous journey from southern China, the ship broke down but managed to limp into Mombasa where it was detained.

But many of the illegal immigrants have been picked up by another ship which is on its way to the US, via South Africa.

About 60 of the 352 migrants are believed to have been caught by the Kenyan authorities.

The migrants are believed to be mostly professionals, although 52 teenage girls on board were said to have been used as sex slaves.

One highly-placed source said: ''Most of them are not from poor families. They are lawyers, doctors, nurses and engineers who seem to have come from rich families and are not willing to go back to China.'' Reports from some Mombasa hotels claim the migrants had plenty of money to spend on phone calls and food when they secretly left the ship.

It is believed the first wave of migrants left the Najd II aboard the Honduran-registered fishing trawler MV Golden Venture, which docked in the high seas.

But because the vessel was overcrowded, about 60 remaining migrants were transferred to the Kenyan tug boat MV Tewa, owned by an engineering company which assisted in refuelling the Golden Venture.

The MV Tewa is believed to have returned to Kenyan waters where it is under guard.

According to US intelligence in Hongkong, the ship heading for South Africa and the second to pick up migrants off Kenya is the same vessel which was last in Thailand where 68 Chinese migrants were arrested trying to board in Pattaya.

The ship, believed to be Thai registered, managed to sail and travelled half full as it was due to pick up the passengers stranded in Mombasa.

A Kenyan Ports Authority manager is suspected to be involved in smuggling the passengers by commandeering a lighthouse to allow the tugs to ferry the Chinese out to the high seas and the mother ship.

The police and Customs Department are also suspected to have been involved with one senior police officer saying it was not their duty to look after the migrants, while a customs officer said he was not aware of their disappearance.

Meetings were said to have been held in Mombasa hotels yesterday to discuss the auctioning of the Najd II to pay outstanding port charges and wages for the ship's 22 crew members, who are sleeping on a badminton court at the Mission for Seamen.

The four agents behind the smuggling - an Italian, Singaporean, Japanese and Korean - are said to have arrived in Kenya about one month ago to arrange for the ship to stop in South Africa, where the migrants have been promised construction work on a floating Chinese restaurant.

US Intelligence reports say two of the agents have left for Cape Town where they will meet an Italian shipping agent who will facilitate the movement of the migrants in South Africa.

There is enough food on board to last three months and it is expected the ship will change its name mid-voyage in an attempt to travel undetected.

This was the second attempt to rescue the stranded Mombasa migrants. Two months ago, a ship called the Ong Brothers attempted to rescue them, but was detained by the Kenyans for defective equipment.

US authorities are monitoring the situation, but after reluctantly becoming embroiled in the East Wood affair, they are unlikely to intercept the vessel.

Meanwhile, an Immigration and Naturalisation Service (INS) agent has warned of the threat to the US from hundreds of illegal immigrants.

She warned that as many as 30 boats could be on their way to the US, a figure many believe to be grossly exaggerated.

''We think it is very serious, that is why we are putting a lot of resources into this,'' she said.

A task force set up last summer to investigate the flood of aliens met last week to discuss the latest developments and exchange intelligence on the maritime racket.

Under Operation Dragon, instituted in 1989, the INS has been responsible for seizing 11 ships and arresting about 1,500 mainland Chinese, excluding the 527 on the East Wood, predominantly from Fujian province.