MAPUTO, Jan 7 (Reuters) - The United Nations said on Monday it would take urgent measures to help victims of deadly floods in central Mozambique that have driven thousands from their homes.

The floods, fed by heavy rains from Zambia and Zimbabwe, have killed six people and cut major transport links to neighbouring countries.

"The humanitarian community stands ready to support the government in the ongoing response," U.N. Resident Coordinator Ndolamb Ngokwey said in a statement.

Waters which had reached a depth of six metres (18 feet) forced some people to seek refuge on trees and rooftops.

Zambia has also been hit by floods, with the government placing nearly half the country on flood alert and farmers expressing fears of crop damage, particularly in the south.

"At least 1.5 million will be displaced by the floods and the government and aid groups will have to provide relief food and shelter to the families in tents for some time," a senior government official said.

Ngokwey said the U.N. had been developing plans to cope with the aftermath of flooding.

"Over the past few months, we have been working closely with national authorities to put in place contingency plans to ensure that needs of those affected by the flooding are met expeditiously," Ngokwey said.

The U.N. noted that heavy rains had led to a sharp rise in water levels in the Zambezi, Pungue, Buzi and Save rivers, and that an estimated 56,000 people have been affected, including 13,000 people who have been relocated to resettlement centres.

In early 2007, floods in central Mozambique killed 45 people and left 285,000 homeless, while cyclone Favio displaced another 140,000 people.

It was the worst flooding to hit the former Portuguese colony since floods in 2000-2001 killed 700 people and drove half a million from their homes.

International aid agencies have expressed concern over erratic weather patterns in southern Africa, which have devastated harvest prospects for millions of people.

Floods have destroyed crops in some parts of southern Zambia and farmers fear that white maize output might fall.

Guy Robinson, president of umbrella farmers group the Zambia National Farmers Union (ZNFU), told Reuters heavy rains had wiped out some plantings. He said the most affected area was southern Zambia, one of the country's major farming regions.

"We are very concerned that the entire crop has been destroyed in some areas due to heavy flooding and it is still raining heavily," Robinson said. (Reporting by Johannesburg newsroom and Shapi Shacinda in Lusaka, Editing by Matthew Jones)

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