Nate was downgraded to a tropical storm early Sunday as it moves farther inland over the US states of Mississippi and Alabama, the National Hurricane Center said.

The storm, which made a second landfall in Mississippi after first hitting Louisiana, was packing maximum sustained winds of 110km/h, and was moving north-northeast at 37km/h, the centre said.

"Nate is expected to continue to quickly weaken as it moves farther inland," the Miami-based centre said in its latest bulletin.

Nate first hit land at the mouth of the Mississippi River, south of low-lying New Orleans in Louisiana, on Saturday evening as a Category 1 hurricane.

It made its second landfall outside Biloxi, Mississippi, at 12:30am (05:30 GMT) on Sunday as a hurricane, with maximum winds of 140km/h.

A hurricane warning was discontinued for the mouth of the Pearl River, which marks the Louisiana-Mississippi state border, to the Alabama-Florida border further east, the agency said.

A tropical storm warning for metropolitan New Orleans was also lifted.

Central America flooding

In Nicaragua, Nate's arrival followed two weeks of near-constant rain that had left the ground saturated and rivers swollen. Authorities placed the whole country on alert and warned of flooding and landslides.

Nicaragua's vice president and spokeswoman, Rosario Murillo, said that at least 11 people had died in that country due to the storm. Earlier Thursday, she had said 15 people had died before later revising to say some of those were still counted as missing.

READ MORE: Nate strengthens to hurricane as it nears US Gulf Coast

She did not give details on all the deaths, but said two women and a man who worked for the Ministry of Health were swept away by a flooded canal in the central municipality of Juigalpa.

Costa Rica's Judicial Investigation Organism blamed seven deaths in that country on the storm and said 15 people were missing. Flooding drove 5,000 residents into emergency shelters.

In Honduras, there were three dead and three missing, according to Oscar Triminio, spokesperson for the country's firefighters.

Damage caused by the storm prompted Costa Rican officials to postpone a World Cup qualifying football match between that country and Honduras, which had been scheduled for Friday night.