LONDON (AlertNet) - Whole villages are on the move in north Yemen, fleeing a widening conflict that is creating a shameful and worsening emergency, aid workers said on Tuesday.

People in the area's main town, Saada, may be worse off still, trapped by shelling and street fighting in homes with barely any water, power or communications and facing food prices spiralling out of reach - if they can make it to market.

"The situation is getting worse and worse and worse. We're not confronted with a humanitarian crisis, it's becoming a humanitarian tragedy," Gian Carlo Cirri, country director for the U.N.'s World Food Programme, told AlertNet by phone from the Yemeni capital Sanaa.

A month ago a new wave of fighting - the "sixth war" in an intermittent five-year-old conflict - erupted in the mountainous north between rebel Shi'ite Muslims and government forces trying to impose central authority.

U.N. agencies estimate this has added up to another 50,000 people to the 100,000 or so already left homeless by earlier rounds of the fighting in the poorest Arab nation. Most of them are women and children.

The United Nations appealed last week for $23.5 million extra to help Yemen - but donors' response so far "has been limited", Cirri said. In July, just before the latest fighting, the WFP had to halve rations for some 50,000 people because money was running out.

The agencies are setting up new camps at a safe distance from the fighting for the lucky ones - those who can reach help.

In a country with strong community ties, many people have found shelter - temporarily at least - with host families, or in mosques and schools, but tens of thousands of others appear stranded in an area whose access roads are blocked, and aid has not reached them for a month.

"Our main concern is access," said Cirri, adding that the WFP was reaching only 10 percent of displaced people in the region.

Some 15,000 people have headed to Baqim, a northern district by the Saudi border. U.N. officials said they were lobbying Saudi authorities to let them open up a supply route through its territory as soon as possible, skirting the conflict zone.

Many aid staff have been pulled out of Saada town, to which an estimated 35,000 new displaced people have flocked. Those staff who remain are pinned down in their homes by the fighting, unable to deliver the stockpiles they have.

Telephone landlines were cut on Tuesday, leaving most people in the area unable to communicate with the outside world. Mobile networks have been out of action since the fighting began.

A truce on Friday to allow aid organisations to deliver food and other vital supplies broke down within hours, scuppering efforts to reach the growing numbers of needy. Each side blamed the other.

Displaced people - and the conflict - have been spilling out into neighbouring regions that lead south towards the capital. Some people have had to move up to four times over the last two years as the fighting moves around.

"We asked for a ceasefire but the clashes continued, and we will reach a really shameful humanitarian situation," Laura Chedrawi, a spokeswoman for the U.N. refugee agency UNHCR, said by phone from a flat, rocky expanse in Amran region near Saada, that from Wednesday will be the area's newest camp.

"Our staff inside (Saada) say the situation on a humanitarian level is a disaster and could get worse by the minute."

She said many displaced people were still on the move seeking safety. Apart from the fighting, reaching them was made harder by a curfew, landmines and other unexploded ordnance on the roads and numerous checkpoints.

WFP officer Maria Santamarina told AlertNet some of the farmers, mechanics and other people she met on a visit this week to another new camp, Al Mazraq, were still full of fear.

Fighting forced most of them out of their mountain village homes with no warning and no time to bring anything with them, to the tent camp in a sparse area with few bushes, no trees, frequent sandstorms and searing heat that was making some of them ill.

They come from an area known for its farming and fruit, especially pomegranates - but also for high malnutrition rates.

The few who had managed to bring their goats with them were now watching them die from the heat.

"Despite the harsh conditions many plan on staying and say they don't want to return because they no longer feel safe," Santamarina said. "They are afraid, they've abandoned homes and farms and some say they fear returning to find nothing left."

Troubled Yemen has also been battling a wave of al Qaeda attacks and rising secessionist sentiment in the south.

No comprehensive casualty figures are available in the northern conflict, and there are few independent accounts of the fighting.

But many civilians have been injured, said Ahmad Al Qubati, Islamic Relief's project coordinator in Saada town until he managed to get out in the last few days, taking a route "across a vast expanse of valleys and desert".

He said his office had shaken with the force of bombing, and continuous shelling boomed all day and seemed to intensify each night.

"During the second week of fighting the army cordoned off parts of the city and ordered residents to leave the old town ahead of intensive bombing, which forced many people to flee their homes," he wrote in a blog, adding that aid deliveries ground to a practical halt.

"Before I left, Saada town was almost empty; people had either fled or were staying inside their homes."

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