(CNN) -- The United Nations and international relief organizations are scrambling to aid Myanmar, saying Friday's cyclone was the worst disaster the country had suffered in years. Myanmar officials expect the death toll to top 15,000.
The cyclone wrecked boats in Yangon Harbor.
The country has "massive, massive" needs, UNICEF spokesman Patrick McCormick told CNN. "I think it's the biggest disaster to hit this country in recent memory."
"The destruction is unbelievable," Dr. Kyi Minn of the Christian relief organization World Vision said from Yangon. "Elderly people are saying this is the worst storm they have ever seen."
The ruling military junta in Myanmar -- traditionally known as Burma -- made a rare appeal for humanitarian aid as it continues plans to hold a referendum Saturday on a draft constitution. But Myanmar experts say government forces are directing efforts to "important" areas first.
"We haven't heard that where the worst-hit areas are getting any aid," said Maureen Aung-Thwin, director of the Burma Project and the Southeast Asia initiative at the Open Society Institute in New York. "We have heard that the government has finally accepted aid, or asked for aid, which is another big deal on their part to have to admit that they need aid."
The United Nations is prepared to send "urgent humanitarian assistance," Secretary-General Ban Ki-moon said, adding he is "very much alarmed by the incoming news" that the government anticipates the count of those killed in Friday's cyclone will top 10,000. Watch how the cyclone crippled Yangon »
The U.N. made $30 million available from its central emergency fund.
A U.N. humanitarian official told CNN International that a five-person disaster response team has mobilized in Bangkok, Thailand, but is awaiting visas to enter Myanmar.
"It's clear that international assistance will be required," said Rashid Khalikov, director of the U.N. Office for the Coordination of Humanitarian Affairs in New York.
"We need to find out more of what actually happened," Khalikov added, saying many roads have been destroyed and communication lines are down. "There is not much information coming out of the affected territories."
Separately, the United States made $250,000 available and offered to send a disaster assistance team, but State Department spokesman Tom Casey said Monday the military junta that rules Myanmar had not given the team permission to enter the country. Learn more about Myanmar »
U.S. first lady Laura Bush, who has a long-standing interest in Myanmar, urged the government to allow the team into the country, saying she expected Washington would provide "substantial" aid if it could conduct its own assessment of the situation on the ground.
And she blasted the junta, saying the lack of warning before a deadly cyclone hit on Friday was the latest example of "the junta's failure to meet its people's basic needs." Watch Laura Bush criticize ruling junta »
Witnesses say state media did report the storm -- it just came too late.
She criticized a draft constitution the government plans to put to its people in a referendum on Saturday, saying pro-democracy activists and some ethnic groups had been excluded from the process of drafting it. She said it would be "very, very odd" if the referendum went ahead as planned this weekend after the devastating storm.
The United States has sanctions in place against Myanmar, whose government is holding Nobel Peace Prize-winning democracy activist Aung San Suu Kyi under house arrest. Casey said the sanctions might restrict what type of donations the United States can make, but will not prevent Washington from sending some type of assistance via the United Nations. See photos of the destruction »
"We are going to make sure whatever we can do to help relieve the immediate suffering of people there is done," he said.
No U.S. ships are close enough to bring relief supplies within days, U.S. Navy officials said, and they have not been ordered to do so. Watch the cyclone hammer Yangon »
Various international organizations have already begun to send aid.
The Myanmar Red Cross has begin distributing what it calls "family kits," and the International Federation of Red Cross and Red Crescent Societies said it will release 2,000 family kits and 2,000 shelters as soon as transport routes are available. The British Red Cross is making about $60,000 available.
World Vision, a U.S.-based Christian humanitarian organization, has appealed for $3 million in donations and plans to send a team into affected areas, spokesman Casey Calamusa said.
"The biggest need is getting water for the 2 million affected people," he said. Since the 2004 Indian Ocean tsunami, which killed as many as 100 people in Myanmar, the isolated country has yet to set up a water purification system.
Church World Service, another aid group, issued an appeal for $50,000 to help disaster victims.
A critic of the military junta that rules Myanmar -- traditionally known as Burma -- said the government does not have the same incentive to accept international aid that a democratic government would.
The people of Myanmar will see it "as the generosity of the international community," said Tion Kwa, an Asia Society fellow based in Washington. "It undercuts the authority of the regime completely.
CNN United Nations Correspondent Richard Roth contributed to this report.