By Daniel Schweimler BBC correspondent in Havana

The Cuban authorities have posted extra police along the country's northern coast amid rumours that large numbers of Cubans are seeking to leave the island on boats that will pick them up from the US.

The Cuban Government has accused Cuban exiles in Miami of encouraging the exodus and warned that it would not allow a boat lift.

More than 50 Cubans have reached Florida in the past week paying up to $8,000 each for the journey

It said that anyone caught sailing to Cuba to pick people up will be prosecuted for trafficking in migrants.

The normally bustling Malecon, the Havana seafront, is almost deserted with policemen standing at regular intervals.

They are watching the coast and the sea that stretches out towards the US, just 150 kilometres (95 miles) away.

Dangerous venture

The Cuban military guard outside the US diplomatic building which is also on the Malecon has been increased.

For the past few days rumours have been circulating around Cuban towns and cities that Cuban exiles in the US will be sending boats to pick up those who wanted to leave the island.

The Cuban Government has warned that it would prosecute anyone it caught for what it calls "migrant trafficking".

The US Coast Guard in Miami has also warned that Cubans could be putting themselves in danger as they try to illegally enter the US by sea.

It is said the Florida Straits is a dangerous, rough area to navigate, especially in overcrowded or unseaworthy vessels.

With the seas a little calmer, there is always an increase in the number of Cubans seeking to escape at this time of the year.

Threat to US mission

The resolve of some has been increased by threats made last week by President Fidel Castro that he may close the US diplomatic mission in Havana, accusing some who work there of sowing discontent among the Cuban people.

Since Mr Castro came to power in 1959 waves of Cubans have on several occasions left the island in large numbers to settle in the US.

The most famous was in 1980 when thousands, including several hundred released from Cuban jails, left from the Western port of Mariel.

The next major exodus was in 1994 but a steady stream leaves almost every week, either on makeshift boats or by buying a place on speed boats that glide in from Miami by-passing the Cuban coastguard.

More than 50 Cubans have reached Florida in the past week, paying up to $8,000 each for the journey.