Bangkok/Yangon -  A desperate international push to get food, water and medicine out to remote areas hard-hit by Cyclone Nargis has run into a basic bottleneck of lack of decent roads and bridges in Myanmar's countryside, aid agencies said Tuesday.

"One of the big limiting factors is that most of bridges in the Irrawaddy Delta are only built to withstand five-ton loads, so we need a large fleet of small trucks," said World Food Programme (WFP) spokesman Marcus Prior.

Cyclone Nargis, packing 200 kilometres-per-hour winds, swept through Myanmar's central coastal region on May 2 to 3, leaving an estimated 100,000 dead and up to 1.9 million in need of basic necessities such as food, water, shelter and medicine.

Much of the destruction was wrought on the Irrawaddy Delta, Myanmar's traditional rice bowl, a low-lying fertile plain intersected by hundreds of rivers and streams, posing a transportation challenge in the best of times.

While trucks, albeit small ones, are now bringing in basic supplies to the main delta towns such as Labutta and Bogale, unknown thousands of people have been stranded in the fingertips of the Irrawaddy without transport.

"There are no roads out there. People get around by boats and now they have no boats because they were destroyed by the cyclone," said Richard Horsey, spokesman for the United Nations Office for the Coordination of Humanitarian Affairs (UNOCHA), that is heading the relief effort in Myanmar.

"With the relief effort not up to speed, people are migrating," said Horsey. The UN estimated that more than a quarter of a million people in the Irrawaddy Delta have been been forced to migrate in the aftermath of Nargis.

Aid workers continued to complain Tuesday about the Myanmar military's slowness in granting visas to UN relief experts who could facilitate and speed up the emergency operation with their expertise.

The UN has been seeking cooperation from the ruling junta in the granting of visas to about 60 key relief experts form the UN and other aid agencies in the military's headquarters in Naypyitaw, 350 kilometres north of Yangon.

"Recent discussion with the government in Naypyitaw suggest that those visas formally applied for through the centralized system will be issued in the coming days," said Prior.

Meanwhile, as hundreds-of-thousands continue to go without food, water, medicines and proper shelter, on Tuesday monsoon rains poured down on much of the area already battered by Cyclone Nargis, adding to the misery.

"These are really desperate times for those people," said Prior.

Meteorologists have forecast that the Irrawaddy Delta will this week be hit by rains equal to all the rainfall in May, last year. (dpa)