Eighteen cockle pickers have died after becoming trapped by rising tides in Lancashire's Morecambe Bay.
Bags of cockles on Morecambe beach as the search mission goes on
The accident happened after more than 30 cocklers - thought to be Chinese who do not speak English - were caught by rising waters in the Hest Bank area.
Lancashire Police said it was trying to find out if they were illegal immigrants or working for an organised gang, and appealed for information.
A spokeswoman added that criminal charges were a possibility.
The 16 men and two women who died were pulled out of the near freezing sea during a huge rescue effort by coastguards, lifeboats and the RAF overnight.
The 14 who survived have been joined by two witnesses thought to be connected to the group and are being cared for at a local emergency centre.
Police said they were of Oriental appearance and they are questioning them with the help of Chinese interpreters.
It is not known whether they were working illegally.
However assistant chief constable Julia Hodson said they were treating the deaths as suspicious.
Asked what view she took of gang bosses who profit from the slave labour of
illegal immigrants, she said: "I think they would be criminals of the worst
possible kind, that are prepared to exploit those that are the most vulnerable
in our communities."
She appealed for help in identifying the victims.
The Bishop of Lancaster, Patrick O'Donoghue, said there was "absolute shock" in the community and called for more protection for migrant workers.
A further body had been spotted in the sea and the search was continuing on Friday afternoon.
It is thought the group set out to go cockling at about 1500 GMT on Thursday, but the tide came in and they got into difficulties. A member of the public raised the alarm at about 2120 GMT.
Ten of the dead, who were in their teens and 20s, were found by an RNLI hovercraft.
Its commander, Harry Roberts, 45, from Morecambe, said: "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.
"They didn't have any safety gear and some of them were naked because they
had taken their clothes off to help them swim."
Morecambe Bay is notoriously dangerous, with fast rising tides and quicksands.
The incident has highlighted local concerns about the huge numbers of outsiders descending on the bay to pick cockles.
Cedric Robinson is known as the Queen's sandpilot in Morecambe Bay, and has been leading walkers across the sands for 25 years.
He said the area was treacherous for people who did not have local knowledge of the tides.
"For strangers to come into the area and go cockling, it is dangerous," he told BBC News 24.
Local MP Geraldine Smith told BBC News 24 that cockling had become "a really controversial issue" in recent weeks.
Survivors were suffering hypothermia-like symptoms
"The problem is Morecambe Bay is a public fishery, so anyone can come and fish," she said.
The estimated value of the cockles on Morecambe beach was £6m, she said, which had lured people from all over the UK and beyond and led to exploitation.
"I'm quite sure those people will have been paid very little for the bags of cockles they collected and the gangmasters will no doubt have made a great deal of money out of them," she told BBC Radio Five Live.
Meanwhile, police in Norfolk are investigating reports that Chinese workers who were living in the Kings Lynn area had moved to work in Morecambe Bay.
Norfolk police ethnic liaison officer Tony Lombari was told by the Chinese community that a large number of workers were moving off to "dig fish".
He said he was trying to establish where they had gone when he heard the news about the cockle pickers' deaths.
Another group of cocklers became stranded in the same area only two months ago - they were all rescued safely.
Police issued two numbers in connection with the incident:
For witnesses or those with information - 01524 63333
For worried relatives - 0870 9020999