Washington: The "potentially catastrophic" hurricane Maria, the strongest storm on record to make landfall in Dominica, has devastated the Caribbean island, the country's Prime Minister said on Tuesday.

The powerful storm, which made landfall at 9.15 p.m. on Monday, has since been downgraded from a Category 5 to a 4 storm with sustained winds of 155 mph, reports CNN.

After it passes over Dominica, it is on course to score a direct hit on the US territory of Puerto Rico, the first hurricane of its strength to do so in 85 years.

"We're just waiting for daybreak to do an assessment of the damage," Dominica Prime Minister Roosevelt Skerrit told CNN on Tuesday morning.

"Our first order of business will be search and rescue to ensure we can account for every single citizen and residents who were on the island during this really devastating hurricane."

A statement from the Washington-based National Hurricane Centre (NHC) said that its record-topping winds reached 160 miles per hour when it hit the island nation.

In an update, the Centre said that reports "indicate significant damage to structures has occurred in Dominica".

Maria was so powerful that it tore the roof off the Prime Minister's residence. "Personally I was affected," Skerrit told CNN.

"The roof of the residence caved in because of the strength of the wind. But I was taken to safe ground by police officers, thank God... I don't think there were very many roofs which would survive the hurricane."

In a Facebook post, he added: "So far we have lost all what money can buy and replace.

"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."

After Dominica, Maria will move towards Puerto Rico as an "extremely dangerous major hurricane, and a warning has been issued", CNN quoted the NHC as saying.

Puerto Rico's Governor Ricardo Rossello has declared a state of emergency ahead of the landfall expected on Wednesday.

US President Donald Trump has issued an emergency declaration for the American territory for federal assistance to augment the island nation's storm-response initiatives.

The storm will also affect parts of the Leeward Islands and the British and US Virgin Islands for next couple of days.

Maria comes after the catastrophic hurricane Harvey made landfall in Texas on August 25 resulting in massive floods and deaths of 83 people.

Harvey was followed by Irma, the most intense storm in the Atlantic. It hit the Caribbean islands on August 30, leaving a trail of destruction through Puerto Rico, Cuba and Florida and killed 82 people.