ABUJA (Reuters) - President Goodluck Jonathan pledged assistance on Tuesday to tens of thousands of Nigerians displaced by the country's worst flooding in five decades.

"Over the past few weeks, unprecedented floods have ravaged many parts of our country, rendering tens of thousands of fellow Nigerians homeless, and causing massive destruction of property, farmlands and infrastructure," he said in a televised address.

"I want to reassure all Nigerians that the federal government is prepared to do everything possible to mitigate the impact of this natural disaster," he added.

Local media have been awash with images of stranded villagers perched on roof tops, buses overturned in flash floods and people traversing waterlogged farmland by canoe.

At least 140 people have been killed around Nigeria and tens of thousands have abandoned their homes since the beginning of July, officials say. The National Emergency Management Agency (NEMA) has called it the worst flooding in 50 years.

In northern Kogi state, NEMA officials have tried to access displacement camps to hand out aid, in some cases by boat. Two weeks ago, large swathes of the oil rich Niger Delta were submerged when Africa's third longest river burst its banks.

There has been no reported impact on crude oil production in Africa's biggest producer. But a cocoa industry body said last month that cocoa output was likely to fall far short of a 300,000 tonne target for the last season because of excessive rainfall.

Jonathan said NEMA had spent 1.3 billion naira ($8.27 million) on relief materials and the ministry of works had spent nearly half that on repairing collapsed bridges and bypasses. He pledged more aid money to affect states.

($1 = 157.1250 naira)

(Reporting by Felix Onuah; Writing by Tim Cocks)