While offers of help poured in, Singapore Air Force Chinook helicopters based in Texas have been airlifting hundreds of residents trapped in New Orleans in the chaotic aftermath of Katrina.

While US President George W. Bush initially politely refused offers of aid, the White House reversed course as the magnitude of the destruction across an area of the Gulf Coast the size of Britain became clear.

The United States on Sunday officially asked for emergency aid from the European Union and accepted assistance from the United Nations.

The Singapore defence ministry Monday said three of the heavy-duty helicopters had so far ferried about 700 evacuees and hauled tons of supplies in 39 sorties.

"The first thing that we noticed was the water level in the city," Lieutenant Colonel Kevin Rodrigues, head of the Singaporean relief mission, told Singapore's Straits Times newspaper. "I think most of the buildings are half-submerged."

Singapore said Monday a fourth Chinook would join the relief efforts.

The CH-47 Chinook helicopters were from a Singapore training detachment in Grand Prairie, Texas.

Katrina slammed into the Gulf coast last week and triggered the worst natural calamity in US history, with the death toll expected to be in the thousands.

Most survivors in the worst-hit city of New Orleans have been evacuated, leaving the once vibrant jazz capital a soaked mortuary of decomposing corpses.

Indonesia, still coping with the aftermath of the December 26 tsunami which left at least 217,000 people dead around the Indian Ocean, has offered to send 40 doctors to help survivors, state media said, quoting a senior minister.

Tsunami-ravaged Sri Lanka said it had donated 25,000 dollars and asked doctors to help.

Neighbouring India, also hit by the tsunami and by floods in Mumbai which left more than 1,000 dead in July, said it would provide five million dollars and medicines to help the United States cope with the massive devastation.

In addition, New Delhi has offered large water purification systems for use in households and small communities in the stricken areas, where potable water is a key concern.

"Having ourselves experienced the tsunami tragedy last year, we can understand the sufferings of the people affected by this natural calamity. Our thoughts and prayers are with them," said India's ambassador to the United States Ronen Sen.

War-torn and impoverished Afghanistan has offered 100,000 dollars in disaster relief aid while Bangladesh, another of the world's poorer countries, said it would donate one million dollars' worth of humanitarian aid.

Pakistan said Monday it has offered to send doctors and paramedics.

Islamabad had received a list from Washington detailing the aid required and was finalising what kind of assistance to provide, the foreign ministry said in a statement.

Among the richer Asian nations and US allies in the region, South Korea offered 30 million dollars in cash as part of its planned humanitarian aid for victims of Katrina, officials said.

Japan has proposed sending an emergency rescue team to help its closest ally and said it was giving 500,000 dollars. The Philippines, which is usually on the receiving end of US disaster assistance, said it would send a 25-member team of aid workers.