Hurricane Joan intensified Wednesday as it headed toward Nicaragua and Costa Rica after causing floods in Colombia that swept away buildings and left an estimated 30,000 people stranded and at least 50 people dead.

Costa Rican authorities declared a state of alert on the country's eastern coast, where they forecast 16-foot waves driven by 110-mph winds.Unconfirmed reports by witnesses in northern Colombia said scores of people were missing in the raging floods and hundreds of homes were buried in mud.

The government said assistance was being rushed to some 30,000 people cut off by floods in towns around Carmen de Bolivar, 406 miles north of Bogota. Police said floods in the area swept away two colleges, a market building and several stores.

Magdalena Montes Peluffo, a lawyer in Carmen de Bolivar, told Radio Caracol in Bogota that up to 100 people disappeared when the River Alferez, swollen by two days of torrential rain, overflowed its banks Tuesday morning.

"The number of dead is very high because the river overflowed at around one in the morning when everyone was sleeping," Montes said, adding that most of the missing are children.

"Many people are homeless because more than 200 houses were totally buried in the mud. This is a very big emergency. A lot of people are crying. The medical teams cannot attend to everyone," Montes said. "It is horrible."

She said firefighters recovered the bodies of two children drowned in the floods and that "a whole district disappeared."

Authorities said heavy rains also caused flooding in La Uribia, 500 miles north of Bogota, and winds ripped off roofs of at least 30 homes in the area.

In northern Guajira Peninsula, near Venezuela, Red Cross and civil defense forces evacuated more than 100 families from flooded towns, police said.

At noon MDT, Joan's center was about 200 miles east southeast of San Andres Island, off the Nicaraguan coast, or 170 miles northeast of Colon, Panama. The system was moving west at 5-10 mph.

It had 110-mph winds, with tropical storm-force winds extending up to 75 miles from the center. Forecasters at the National Hurricane Center said additional strengthening was possible through Thursday.

Authorities warned vessels against heading into the choppy Caribbean, and in Cartegena, 420 miles north of Bogota, people were told not to swim.

"It's really too early to say where it's going to cross _ it's headed on a very open path _ but we can say it is moving toward the Costa Rican and Nicaraguan coasts," said weather specialist Brian Maher at the National Hurricane Center in Miami.

The storm was named Joan on Oct. 11 and was declared a hurricane Monday night. It grew from a depression that formed 1,000 miles east of French Guiana, on the northeastern coast of South America.

Joan was the fifth of 17 tropical depressions to grow into a hurricane at 74 mph during the 1988 Atlantic-Caribbean hurricane season.