Over 1,000 turtles have already died

"It's getting too cold, many are injured and we don't have the medical expertise to rescue so many. I am afraid many will die if they don't get proper help soon," said a spokeswoman, Idy Wong.

Some tropical turtles are currently living in open pig-pens with temperatures falling below 7C.

About 450 turtles were given free passage on United Airlines flights on Thursday and Friday to the Alapattah Flats Turtle Preserve in Port St Lucie in Miami.

Now Ms Wong is appealing for cargo space to transport 6,000 remaining turtles.

The turtles which have arrived in Miami will be treated and catalogued, before being found new homes by the Turtle Survival Alliance, the animal rights group which has organised the operation.

Meat trade

"The species we're working with, under the best of circumstances, have a heavy mortality rate, so we're not sure how things are going to look tomorrow morning," said the head vet for the rescue mission, Barbara Bonner.

The Hong Kong centre does not have enough space

The consignment of 10,000 turtles, 90% of which are classed as "critical", "endangered", or "vulnerable" species, was estimated to be worth $3.2m.

It included some of the most endangered species in the world, such as the river terrapin, Asian brown turtle, painted terrapin, box turtle and the black marsh turtle.

The reptiles were destined for dining tables in China, where demand is so high that local populations have been exhausted and importers look to countries such as Vietnam and Bangladesh to meet demand.

Conservationists say the animals were travelling in appalling conditions, stacked in styrofoam and cardboard boxes, with the creatures at the bottom of the crates supporting the weight of thousands of others above.

"When we opened up the boxes, turtles at the bottom of the pile were completely smashed," said Ms Wong.