Aid agency the International Organization for Migration sounded the alarm Tuesday over a drought in the Marshall Islands, one of the world's remotest ocean communities, warning that thousands of people were at risk.

"Officials have found some families living on a gallon, or 3.8 litres, of water per day -- barely half of the international standard for emergency water requirements, and often the precursor to serious health conditions," IOM spokesman Jumbe Omari Jumbe told reporters.

Lying in the northern Pacific Ocean, midway between Hawaii and Australia, the republic formed by more than 1,000 islands has faced unusually low rainfall since February.

The crisis has led the government to declare a state of emergency in the northern atolls which are home to around 3,200 of the Marshall Islands' 52,558 people.

"Food security is a major concern, as crops, plants and trees have been damaged," Jumbe said.

Government aid ships have begun transporting US-donated supplies, including water containers and hygiene kits, from IOM warehouses, he said.

"While this may not be a massive disaster in global terms, it is highly significant for this remote and fragile environment," Ashley Carl, the IOM's chief of mission for the Marshall Islands, said in a statement.

Island nations are seen as a touchstone of environmental crisis, as sea levels rise in the face of global warming, leading to predictions that many such communities will be forced into exile in coming years.