YANGON, Myanmar (CNN) -- The U.N. says hungry crowds of survivors have stormed shops that reopened Wednesday in Myanmar's devastated Irrawaddy delta, with little aid reaching the area since a weekend cyclone killed more than 22,000 people.
Paul Risley, a spokesman for the U.N. World Food Program in Bangkok (WFP), Thailand, told The Associated Press that aid workers had reported "fist fights are breaking out" after a few shops had reopened.
The delta, Myanmar's rice-growing heartland, has been devastated by Cyclone Nargis, threatening long-term food shortages for survivors, experts said.
The Rome-based U.N. Food and Agriculture Organization (FAO) estimates that five states hit hardest by Saturday's cyclone produce 65 percent of the country's rice, AP reported.
The region was also home to 80 percent of its aqua culture, 50 percent of its poultry and 40 percent of its pig production, the FAO said.
Rice is the most important staple in the impoverished country, which has produced enough to feed itself and, more recently, stave off rising prices.
"There is likely going to be incredible shortages in the next 18 to 24 months," Sean Turnell, an economist specializing in Myanmar at Australia's Macquarie University told AP. "Things will be tough."
WFP, which has started feeding the estimated one million homeless, said there were immediate concerns about salvaging harvested rice in the flooded Irrawaddy delta, known as the country's rice bowl.
The cyclone, which battered the country last weekend with winds of 240 km/hr(150 mph) and 3.5 meter (11.48 feet) storm water surges, killed more than 22,000. Another 41,000 people are still missing, according to state-run media outlets in Myanmar, and the U.N. estimates one million could be homeless.
Damage was also extensive in the country's largest city, Yangon. Much of the former capital is without power and littered with debris and fallen trees.
Harrowing details have started to emerge, with one woman describing to the Democratic Voice of Burma -- a broadcast media group run by opposition expatriates -- a wall of water jumping from the Gulf of Mottama into the delta areas.
CNN obtained the video in which the survivor said she walked a trail dotted by dead bodies to get to safety, passing a group of about 1,000 homeless people who slept on the street. See photos of the destruction »
"Yes, there is tide coming along. Trees fall over people," the survivor said. "There are many dead bodies lying under trees. Yes, all people I saw are crying too much and searching for bodies of loved ones. There is bad smell from dead bodies on the way we came from."
The woman said she lived in the village of Dadaye near the gulf in southern Myanmar, which was in the path of the storm. She said that as she fled, she passed a village where only six people survived.
"We found about 40 dead bodies on this way," the woman said. "Everywhere ... in the bushes like this, and in the streams like this. Everywhere."
CNN's Dan Rivers, the first Western journalist into the devastated town of Bogalay, reported seeing bodies being thrown into rivers by survivors in desperate need of help.
Rivers said Wednesday that it was difficult to find the words to describe the level of destruction.
"Ninety percent of the houses have been flattened... the help that these people are getting seems to be pretty much nonexistent from what we've seen."
Rivers said he saw members of Myanmar's army clearing roads, but handing out little food or medicine.
"There has been scant help really. I think we saw one or two Red Cross vehicles in the entire time we were driving," he said of his travels over a 12-hour period.
The aftermath has pushed Myanmar's normally secretive ruling military junta to ask for aid and release details of the devastation.
WFP said it had begun distributing food in areas of Yangon and was preparing to send emergency supplies from across Asia.
However, international efforts to provide assistance were being frustrated by Myanmar's delay in processing visas for aid workers.
"We've got stuff on standby and we expect in the next day or two to be given the go-ahead," James East of World Vision told CNN from Bangkok, a staging area for many groups.
Hundreds of World Vision staff were already in Myanmar with limited supplies, according to East, distributing food and water, and making assessments.
He said it wanted to bring in additional employees and supplies "as soon as possible."
East said the big challenge was getting the aid to the people who needed it.
"Even when aid comes in, it's going to be a logistical nightmare to get it out to the remote delta region," he said.
Andrew Kirkwood, head of the Save the Children aid group in Yangon, said people were getting sick.
"The whole place is under salt water and there is nothing to drink. They can't use tablets to purify salt water," he told AP.
The Myanmar Red Cross has been handing out relief supplies, such as clean drinking water, plastic sheeting, clothing, insecticide-treated bed nets to help prevent malaria, and kitchen items, the International Federation of Red Cross and Red Crescent Societies said.
President Bush called on the military junta Tuesday to allow the U.S. to help with disaster assistance.
The U.S. has pledged $3.25 million and offered to send U.S. Navy ships to the region to help relief efforts -- if Myanmar's government agrees.
Several other countries and world bodies, including Japan and the European Union, have pitched in. Most recently, Australia's government pledged $2.8 million for aid.
Based on a satellite map made available by the U.N., the storm's damage was concentrated over about a 30,000-square-kilometer area along the Andaman Sea and Gulf of Martaban coastlines, home to nearly a quarter of Myanmar's 57 million people.
The country's state radio said Saturday's vote on a military-backed draft constitution would be delayed until May 24 in 40 of 45 townships in the Yangon area and seven in the Irrawaddy delta, AP reported.
The constitutional referendum is referred to in the state-run media as the fourth step of a "seven-step road map to democracy."
Myanmar, formally known as Burma, last held multiparty elections in 1990, when Suu Kyi's National League for Democracy handily won. The military junta ignored the results.