By Allan Seccombe
MAPUTO, March 21 (Reuters) - The Mozambican government put flood-battered towns north of the capital Maputo on maximum alert on Tuesday as fears rose that swollen rivers could burst their banks again after heavy rains, aid agencies said.
"The government has issued a maximum alert for the people living in the Limpopo River region, but luckily a lot of people have not moved back into their homes yet," said Ian MacLeod of the U.N. Childrens' Fund.
The alert came just hours ahead of a fresh appeal for assistance by the Mozambique government after the widespread destruction in more than a month of flooding since mid-February.
The floods -- Mozambique's worst natural disaster -- have left some 500 people dead and driven 450,000 more from their homes, prompting a huge international relief effort to provide food, medicine and shelter.
"I don't think there is any need for rescue operations. It is not as dramatic as before. Hopefully what will happen is that despite there being a lot of water, it won't have the same effect as the end of February," MacLeod told Reuters.
There have been heavy rains in north eastern South Africa and Zimbabwe and rivers flowing east to form the Limpopo and Incomati Rivers, which empty into the Indian Ocean, could potentially flood towns that were devastated in February.
Aid organisations say the new wave of water could hit the area within 48 hours.
The United Nations World Food Programme (WFP) says about 100,000 people could be affected in the Limpopo River valley. The town of Xai-Xai near the river was one of the worst affected in February and is still under water.
"We sent an aircraft to assess the rivers and the crew reported that the Limpopo River is flowing rapidly, but it hasn't risen significantly yet," said WFP's spokeswoman Abby Spring.
"The WFP is concerned water could rise in Chokwe and Xai-Xai and cause problems," she said, adding that rains over southern Mozambique had cut off a main road used to deliver food to the region and could take 10 days to reopen.
"We will have to rely on helicopters again," she said.
Helicopters can't carry the same amount of aid as trucks. The relief operation has at its disposal 31 helicopters and 16 fixed wing aircraft.
United States Air Force spokesman Lieutenant Colonel Tom Dolny said two helicopters were on standby at Maputo airport as part of a regular procedure to deal with emergencies.