The 54 men and four women are thought to have been illegal immigrants and reports suggest they are of Chinese origin. Two survivors, both men, have been taken to hospital.

The lorry had travelled to Dover from Zeebrugge

Home Secretary Jack Straw said he was appalled by the loss of human life caused by what he called "the evil trade in trafficking". He will make a statement to the House of Commons this afternoon.

Amnesty International described the deaths as "a tragedy waiting to happen", and said it highlighted the desperate lengths some people were willing to go to enter the UK.

A Customs and Excise spokeswoman said the bodies were discovered by a single officer during a routine search of the lorry.

She said the officer was traumatised and had already undergone counselling to cope with the shock.

Major investigation

The bodies have been taken to a temporary morgue where post mortem examinations will be carried out.

Mark Pugash, of Kent Police Media Services, said a major criminal investigation had been launched.

"Part of the investigation is to trace back the journey of those who died," he said.

He said it was still too early to say how the people died, but officers have not ruled out the possibility that the victims suffered carbon monoxide poisoning or suffocated.

He confirmed that the lorry was an airtight 18-metre-long container which was only partially loaded with fresh tomatoes.

Its refrigerating unit was not switched on and it remains unclear what the interior temperature would have been.

The scale of this takes your breath away

Gwyn Prosser Dover MP

Gwyn Prosser, Labour MP for Dover and Deal, said he was stunned by the tragedy.

"It emphasises the awful desperation some people must be experiencing to take the chances they take to come cross the channel on the backs of lorries," he said.

Mr Prosser said dead stowaways had been discovered before in lorries entering Dover.

"But the scale of this takes your breath away," he said.

Nick Hardwick, chief executive of the Refugee Council, described those responsible for trafficking as "reckless, callous international criminals".

A criminal investigation has been launched

He told the BBC: "Unless there's a much better system for managing migration overall then people will go on putting themselves in these very dangerous situations."

Mr Straw, who oversaw the arrest of immigrants arriving in lorries in Dover in April, said his thoughts were with the relatives of those who have perished.

"The government is determined to continue to crack down on the evil trade in such trafficking, whose perpetrators have no regard for human life," he said.

Shadow home secretary Ann Widdecombe said one of the real problems was catching the criminals who are organising the trafficking of immigrants.

"A great many of them are operating from abroad," she said.

'More co-operation needed'

"There is a great case for more international co-operation."

The government has recently taken action over the large numbers of illegal immigrants coming through British ports.

Among the new initiatives include �2,000 fines for anyone caught with stowaways and the creation of detention centres to hold asylum applicants while their cases are being considered.

Truck drivers at Dover expressed shock but not surprise at the grisly discovery of bodies.

One driver, Simon Lawton, 40, from Leeds, said people had tried to stow away in the side boxes of his refrigerated trailer while he was working in Greece.

"They thought I was coming to England but I was actually going to Athens," he said.