Several hundred illegal immigrants from Haiti are being detained outside Miami after making a dramatic dash from an overcrowded boat onto a busy highway late Tuesday.

Federal and local officials scrambled to round up the Haitians and eventually loaded them onto buses for transport to a U.S. Immigration detention center. Several Haitians were treated for dehydration and one pregnant woman has been hospitalized.

Earlier, pandemonium erupted when an estimated 200 Haitians jumped from an 18-meter boat and swam to shore along a causeway between Miami and Key Biscayne. Stunned motorists found themselves under siege as scores of new arrivals attempted to pile into their vehicles and flee the scene.

U.S. Coast Guard spokesman Luis Diaz said the immediate concern was for the wellbeing of the Haitians.

"The boat beached itself and hundreds of people jumped over the side," he explained. "Many made it ashore and were detained. Others were plucked from the water by Coast Guard rescue units."

Miami's police force closed the causeway for several hours while U.S. Border Patrol and Immigration agents rounded up as many of the Haitians as possible. Police officials say it is possible that some of the Haitians escaped, possibly with the assistance of motorists.

Boats overcrowded with Haitians periodically arrive in Florida. Those who land on U.S. soil are entitled to an immigration hearing, but the vast majority of Haitian rafters are regarded as economic - not political - refugees, and eventually repatriated.

Tuesday's incident did not go unnoticed by Miami's large Haitian-American community, which mounted an informal demonstration later in the day.

One protester said Haitians who flee their country should be welcomed, not shunned, by the United States.

"They come to work; they want to work and make a better life," said the protester. "We are going to be here [protesting] all night until we get justice. We need justice."

Tens of thousands of Haitians took to the seas in hopes of reaching the United States in the mid-1990s. U.S. officials say they hope to avoid a repeat of the chaotic mass exodus, adding that those who wish to come to the United States should do so legally, and apply from their country of origin.