Otto, a storm swirling in the Caribbean, regained hurricane strength Wednesday as it headed towards the coasts of Costa Rica and Nicaragua, the US-based National Hurricane Center said.

The storm, which has prompted evacuations and emergency alerts, was packing maximum sustained winds of 75 miles (120 kilometers) per hour as it spun about 140 miles northeast of Costa Rica's Caribbean port city of Limon, the monitor said in its latest bulletin.

Otto had strengthened into a hurricane Tuesday, only to be downgraded back to a tropical storm.