The US has ships with aid standing by in the Gulf of Thailand
UN Secretary General Ban Ki-moon has warned of dire consequences if Burma continues to ban most foreign aid workers from its cyclone relief work.
Speaking before the UN launched its $187m (£96m) appeal to help those hit by the cyclone, he said early action was needed to prevent catastrophe.
Burma, where the UN fears the death toll could reach 100,000, says it will accept aid from any quarter.
A Burmese constitutional referendum scheduled for Saturday is going ahead.
Polls opened early on Saturday in all but the worst-affected areas, which will vote on 24 May, and are due to close at 1600 (0930GMT).
The country's ruling generals say the referendum will pave the way for democratic elections in 2010, while the opposition says it is intended to tighten the generals' rule.
People were voting in small numbers, correspondents say
They have been criticised for their handling of the crisis in which officially 23,335 people were killed and 37,019 are missing.
The cyclone left towns flattened, infrastructure destroyed and 5,000 sq km (1,930 sq miles) of farmland in the Irrawaddy delta under water and littered with dead bodies.
There are reports that a senior general over-rode requests from his officers to divert army resources to help the cyclone victims - in order to maintain security for the poll.
Reporting on the referendum from Hlegu, a town 48km (30 miles) north of Rangoon, the Associated Press says turnout has been very light, with people coming to polling stations in small groups and no sign of long queues.
One voter, retired soldier Nyo Aye, said he had voted Yes even though he had not read the constitution.
"The government would not do anything inappropriate or bad for the country," the 65-year-old said.
Groups involved in last year's pro-democracy protests accused the junta of concentrating on a "sham constitutional referendum" instead of "putting all resources toward saving the lives" of cyclone victims.
Aid agencies already in Burma say they have been doing what they can but are frustrated by the government's reluctance to allow international aid teams into the country and its insistence on distributing aid itself.
The sheer survival of the affected people is at stake
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