Speculation was mounting last night that 19 cockle pickers who drowned after they were trapped by racing incoming tides were exploited migrants working for ruthless gangmasters.

The victims - 17 men and two women - were among a group of mainly Chinese workers harvesting cockles in Morecambe Bay, Lancashire.

A frantic rescue mission involving two RAF helicopters and numerous lifeboats was launched when the alarm was raised shortly after 9pm on Thursday.

Sixteen people escaped the deadly waters, which fill the bay faster than a man can run when the tide races in.

Police were last night questioning the survivors with the help of Cantonese and Mandarin translators.

Among them are two white Europeans, nine asylum seekers and five people previously unknown to the immigration services. Four of them have since claimed political asylum.

Assistant Chief Constable Julia Hodson said the non-European survivors were "mainland Chinese nationals".

She said: "We still do not know if the people involved are illegal workers.

"We don't know if they had the required permits or if they were working for anybody else. These are lines of inquiry that are still being pursued."

Asked for her opinion of gang bosses who profit from the "slave labour" of illegal immigrants, she said: "They would be criminals of the worst possible kind."

During Thursday night, rescuers began ferrying bodies back to shore from a sandbank in the northern part of the bay, several miles from Hest Bank where the group was reported missing.

One rescuer described the harrowing job of recovering the bodies of the men and women, who were thought to be in their teens and 20s.

RNLI rescue hovercraft commander Harry Roberts, 45, said none had any safety gear and some had stripped naked as they tried to swim to safety.

He said: "The first body was recovered by the RAF Sea King helicopter. We then found one body followed by a group of nine.

"It was very distressing but we were doing the job we were trained to do. It is the worst tragedy I have come across in my time with the RNLI."

The dead were taken to the RNLI station on Morecambe's seafront before being taken by ambulance to a mortuary.

Survivors were wrapped in silver emergency blankets and driven away by police.

Two were taken to Lancaster Royal Infirmary for treatment while the others were held at Lancaster police station.

Morecambe Bay is notoriously dangerous, with fast rising tides and quicksands.

Stewart Rushton and his nine-year-old son, Adam, died in the flats two years ago after becoming disorientated in fog and trapped by the rapidly incoming tide.

Mr Roberts said the rush by gangs of immigrants to harvest the shellfish had been a "tragedy waiting to happen".

Mr Roberts said that about 500 people a day flocked to the area to pick cockles.

It is thought the group was about one mile out when the water came in and they found themselves stranded.

The Bishop of Lancaster - who heads the Catholic Church's migration policy - demanded more protection for migrant workers in the wake of the disaster.

TUC General Secretary Brendan Barber said: "Whatever the legal status of these workers, they should not have been working in such dangerous, unsupervised conditions.

"The full force of the law must be brought against those responsible for their deaths."