Ivan, a dangerous Category 4 storm on a five-step scale of hurricane intensity, slammed into Grenada, a volcanic island of 90,000 people in the southeastern Caribbean on Tuesday, flattening or badly damaging homes and cutting power.
"Our diplomats are reporting that there are 20 confirmed deaths," said a US State Department official in Washington.
The airport in the former British colony was closed and the phone service was interrupted, so the extent of the damage began to emerge only on Wednesday.
A videotape shot from a British naval helicopter showed widespread destruction with buildings flattened, roofs ripped off houses and major flooding.
Grenada's capital, St George's, was devastated. The storm destroyed the island's emergency operations centre, the prime minister's residence, the prison, many schools, and damaged the main hospital.
"I can estimate about 85% devastation," Kenrick Fullerton, a member of parliament in Grenada, told a radio station in Trinidad.
Crews cleared the airport runway so emergency flights could land, but looting broke out and the Caribbean Disaster Emergency Response Agency urged aid groups to send only essential personnel until police could guarantee their safe passage.
"I can estimate about 85% devastation"
A member of parliament in Grenada
Police, troops and ham radio operators were en route from neighbouring islands to help relieve what CDERA called a serious security situation. "There is some looting in the capital city, so I think that is causing some concern," said a CDERA manager Donovan Gentles.
The latest in a busy Atlantic hurricane season, Ivan prompted storm alerts for the Dutch islands of Aruba, Bonaire and Curacao, the north coast of Venezuela, Colombia's Guajira peninsula, Jamaica and parts of Haiti and the Dominican Republic. Its winds hit 232 kph and it was expected to strengthen.
Grenada is a major nutmeg producer with an area of 344 sq km. A local television journalist told a Trinidad radio station that one area of nutmeg production was completely destroyed.
"Here in (St Andrew), the nutmeg industry in Grenada is gone. This is one of the nutmeg belts in the country and people are wondering about their livelihood," said Ejenny Mason. "Most of the houses have either been flattened or have lost their roofs."
Trinidad prepared to send two ships with relief supplies and troops to help rebuild on the island, which became known when the United States invaded it in 1983.