MANAGUA (AFP) - A tropical storm churning north along Central America killed at least 20 people in Nicaragua, Costa Rica and Honduras on Thursday (Oct 5), with forecasters predicting it could strengthen into a hurricane as it heads for Mexico and the United States.

The state of Louisiana and the city of New Orleans are preparing for a weekend impact from the storm, which could be the third hurricane to hit the southern US in less than two months.

Costa Rica declared a national emergency, closing schools and government offices. It and neighbouring Nicaragua struggled with mudslides, washed out roads, overflowing rivers and cut-off communities.

Nicaragua's vice president, Rosario Murillo, sharply revised upwards a previous toll to say 11 people had died in her country. Seven more were missing, she said.

Officials in Costa Rica said at least six people died there: four Costa Ricans - including a three-year-old girl - hit by falling trees and mudslides, and two young Nicaraguan farm workers. At least another 15 people were missing, including the crew of two swamped fishing boats, police said.

In Honduras, officials said three people had died.