The Burmese government has raised its estimate of deaths after last weekend's cyclone to 28,458 dead and 33,416 missing.
Most of the victims were killed by the 3.5m sea-water surge that hit the delta along with the Category 4 cyclone's 190km/h winds.
But the UN Office for Coordination of Humanitarian Affairs said the deaths could be in the range 63,290 to 101,682, and 220,000 people are reported to be missing.
The UN humanitarian agency said 1.2-1.9m people were at risk in the aftermath of the storm.
In a blow to the stumbling relief effort, a boat carrying some of the first aid to survivors sank, the International Federation of Red Cross and Red Crescent Societies said.
The boat was believed to have hit a submerged tree in the Irrawaddy delta.
France is set to deliver 1,500 tonnes of rice aid aboard the warship Mistral, which should arrive in Burmese waters in the middle of this week.
A cargo plane chartered by the International Committee of the Red Cross carrying 35 tons of aid for cyclone victims has landed in Burma's biggest city.
The ICRC said the medical supplies on board were sufficient to treat some 250 trauma patients and provide three months of basic health care for 10,000 people.
The plane was also carrying sanitation equipment, including a mobile water-treatment plant to provide drinking water for 10,000 people.
The military government was pressing on with the weekend referendum on a new constitution.
There is no indication yet of when results will be released, as balloting was delayed by two weeks in the worst-hit areas, including the former capital, Rangoon.
