BANGKOK (AFP) - - A few aid shipments had arrived in Myanmar's main city by Thursday, but the planeloads of supplies and heavy equipment needed to help millions of cyclone victims remain largely stranded outside the country.

entire families were wiped out In a dramatic development, the ruling junta agreed to accept US emergency aid after last weekend's cyclone, allowing at least one military plane to deliver supplies to Yangon.

Aid But the secretive regime's reluctance to allow foreign experts and other dedicated relief flights into the country has caused intense frustration and compounded the misery for a million people homeless and short of food and water.

Without transport and fuel, aid arriving piecemeal on commercial flights into Yangon cannot be distributed effectively in the devastated Irrawaddy Delta region in southern Myanmar, which was submerged in Saturday's cyclone.

"The bottle-neck is getting (aid) out in the delta. That needs boats, helicopters, trucks... there are upward of one million people in need of help," said UN spokesman Richard Horsey.

Horsey, from the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), said about 5,000 square kilometres (1,930 square miles) of the cyclone-hit region remains underwater.

And he confirmed that while some shipments have arrived over the past two days, no dedicated aid flights have landed in Yangon.

"UN aid has begun to arrive in Yangon by cargo plane," he said. "Some have come in on Thai commercial flights, Thai cargo flights. More is expected today."

Even if they win permission to launch a full-scale relief effort, aid organisations face tremendous logistical problems including flooded roads, scarce fuel supplies, and a shortage of boats as many were destroyed in the storm.

UNICEF spokeswoman Shantha Bloemen said the UN's children's fund was having to distribute the supplies it had in Myanmar by road into the disaster zone, and was relying heavily on the resources of the Myanmar Red Cross.

"The biggest concerns at the moment are those areas that haven't been reached and the more than 200 temporary shelters getting congested, where people have gathered without clean water and sanitation," she said.

"You need people to coordinate where the equipment is going, there are complicated logistics involved," she said. "And how it will work... this is what doesn't seem clear yet."

Horsey said that without immediate assistance, the death toll -- officially at nearly 23,000 with more than 42,000 missing -- would climb.

"We have to be fearful that most of these (missing) people will be dead," he said, adding that the thousands of bodies rotting in floodwaters posed a grave health risk to survivors.

Condoleezza Rice "Fairly clearly, we're dealing with a situation where there could be a second round, where people start dying from water-borne diseases."

military junta The United States and France have both offered to send naval ships, currently on exercise in the region, but their offers remain unanswered on Thursday.

OCHA has said that some of its experts are scheduled to travel to Myanmar aboard a relief plane which was due to leave Italy with 25 tonnes of aid on Wednesday but still has not departed.

specific help The World Food Programme said it was sending several aircraft loaded with high-energy biscuits and other critical supplies -- which would be the first to land into the city -- but their arrival had not been confirmed Thursday.

The UN refugee agency said Wednesday that 22 tonnes of supplies were stuck at the border with Thailand, waiting for the authorities in Yangon to allow the aid to enter the country.

Horsey said visa restrictions are hampering the plans of dozens of experts from the United Nations and other civil society groups who are still working on breaking through government red tape.

"That's a great concern because these are the people ... who are very experienced operating in relief situations," he said.

India UN chief Ban Ki-moon and US Secretary of State Condoleezza Rice have led calls for Myanmar's generals, who deeply mistrust most of the outside world, to admit international disaster relief.

ASEAN "It should be a simple matter. It's not a matter of politics. It's a matter of a humanitarian crisis," Rice said.