Dominica has suffered "widespread damage" from Hurricane Maria, Prime Minister Roosevelt Skerrit says.
"We have lost all that money can buy," he said in a Facebook post.
The hurricane suddenly strengthened to a "potentially catastrophic" category five storm, before making landfall on the Caribbean island.
Earlier Mr Skerrit had posted live updates as his own roof was torn off, saying he was "at the complete mercy of the hurricane".
"My greatest fear for the morning is that we will wake to news of serious physical injury and possible deaths as a result of likely landslides triggered by persistent rains," he wrote after being rescued.
Maria is moving roughly along the same track as Irma, the hurricane that devastated the region this month.
It currently has maximum sustained winds of 250km/h (155mph) and has been downgraded to a category four hurricane, but it could increase again as it moves towards Puerto Rico and the Virgin Islands, according to forecasters.
Dominica's PM called the damage "devastating" and "mind boggling".
"My focus now is in rescuing the trapped and securing medical assistance for the injured," he said, and called on the international community for help.
"We will need help, my friend, we will need help of all kinds," he said.
Curtis Matthew, a journalist based in the capital, Roseau, told the BBC that conditions went "very bad, rapidly".
"We still don't know what the impact is going to be when this is all over. But what I can say it does not look good for Dominica as we speak," he said.
All ports and airports are closed and residents near the coast have been ordered to go to authorised shelters.
The nearby island of Martinique has declared a maximum-level alert while another French island, Guadeloupe, ordered evacuations.
Hurricane warnings are also in place for:
Puerto Rico: The US territory expects Maria to make landfall as at least a category three storm later on Tuesday. It escaped the worst of Irma and has been an important hub for getting relief to islands more badly affected. Governor Ricardo Rossello urged islanders to seek refuge
US Virgin Islands and British Virgin Islands: Both island chains suffered severe damage from Irma and President Donald Trump declared a state of emergency for the US territories on Monday. British authorities fear debris left behind by Irma could be whipped up by the new storm and pose an extra threat.
Warnings are also in effect for St Kitts and Nevis, Montserrat and St Lucia while hurricane watches are in place for St Martin, Saba, St Eustatius and Anguilla.
The British government said more than 1,300 troops were staying put in the region and an additional military team had been deployed to the British Virgin Islands where entire neighbourhoods were flattened by Irma.