How many people have to die before people realise that paying a smuggler is paying to put people in grave danger?

Gene Smith, US Coastguard

Each of the immigrants had reportedly paid $10,000 for their place on the boat, which set off from Cuba on Saturday evening and was expected to arrive in the Florida keys on Sunday.

When the boat failed to arrive as planned anxious relatives in Miami waited a further 24-hours before contacting the American authorities for fear of prosecution.

As soon as they did, a full scale rescue operation was launched involving the US Coastguard and US Air Force. Late on Tuesday night they found a vessel matching the boat's description floating upside down.

No sign of passengers

A single life-jacket was floating nearby, but there was no sign of those on board.

"Pending further developments, we have exhausted all hope of finding anybody," coastguard spokesman Gene Smith said.

The smugglers fee is well beyond the means of most Cubans

The sinking is the single worst smuggling tragedy ever from Cuba - according to the Miami-based relatives of the missing there were 30 people on board, including a dozen children.

Federal prosecutors in south Florida are investigating the incident, hoping to find the organisers of the voyage, who could face charges of smuggling illegal migrants.

Perilous journey

Mr Smith said the boat probably hit high seas.

"A 30-foot (9m) boat in 14-foot (4.5m) seas, that's just crazy, it's really dangerous, and this is a 30-foot boat with 30 people on board," Mr Smith said.

"How many people have to die before people realise that paying a smuggler is paying to put people in grave danger?" he asked.

The flimsy boats are often dangerously overcrowded

The charge for the trip, up to $10,000 a head, is far beyond the means of most Cubans on the island, and so it is usually paid by relatives in the US.

Carlos Montane, whose ex-wife and eight-year-old daughter were on board the boat, said he paid the fee for their passage.

"I can't live all my life with this guilt," he told the Miami Herald.

The US Coastguard say their search for the missing will continue and again warned Cubans of the dangers of trying to enter the country in this way.