By Skye Wheeler

JUBA, Sudan, July 30 (Reuters) More than 12,000 people have been affected by flooding in southern Sudan, emerging from decades of civil war, and six of the region's 10 states have been declared a disaster zone, officials said today.

South Sudan's Vice President Riek Machar declared the disaster zone. At least two people have been reported killed by the rains and flooding, said Lydia Poole, a U N emergency response official.

Poole said the final figure of flood victims would likely be much higher.

''Responding is going to be extremely challenging logistically and very expensive,'' said Poole, adding at least 1,000 people were stranded in one hard-to-reach area.

In northern Sudan, the central government said 59 people had been killed and more than 100 injured in flash floods, which have spread to most parts of the country.

U N stockpiled resources in poorly accessible areas are dwindling and new appeals for help are being written.

Despite a lack of information from the vast reaches of the swampy south, dotted with villages, the United Nations and the southern government are braced for more flooding.

The Government of Southern Sudan (GOSS) has allocated 1 million dollars to the worst two affected states said James Kueth, relief director for the GOSS humanitarian wing.

Kueth, who said most of those affected had been displaced, said the central Khartoum government had contributed blankets and plastic sheeting to the two worst affected states.

U N analysts say new road construction following the signing of a north-south peace deal in January 2005 has changed drainage patterns and is partly responsible for changed water movement.

REUTERS JT HT2158