Most of them arrived in tractors or trailers, which they had to leave behind at the border.

They said Serbian police and paramilitary units had forced them out of the town of Slatina, about 30 kilometres north of the border, at short notice.

The BBC's Orla Guerin: The faces tell of terror, misery and shock

One girl of 18 said many of them had been beaten and threatened by police with automatic weapons.

Aid workers believe there are as many as 5,000 to 6,000 more people on their way to the border.

(Click here to see a map of the most recent refugee movements)

BBC Correspondent Jim Fish says Serbian authorities seem to be sending the deportees through in waves of 1,000 or more at a time.

The BBC's Jim Fish: The first time refugees have arrived at night

Most of the people who have been arriving in Macedonia in the past few days have spent several weeks on the move inside Kosovo.

Many say they have run out of food and cannot buy supplies in the shops.

For the past few days, they have been arriving at the border by train during the day. Aid officials fear this unusual night-time expulsion could be the prelude to more mass movements.

The BBC's Jacky Rowland: The conditions in rural areas are fairly relaxed

But BBC Correspondent Jacky Rowland, who has been travelling inside Kosovo, says the situation of displaced people is more complex than is usually reported.

There are a number of places where displaced Kosovo Albanians have been able to settle, apparently without harassment from Serbian security forces. This is in sharp contrast to reports of massacres heard from many refugees fleeing to Albania and Macedonia, our correspondent says.

Refugee agency 'needs support'

The UN refugee agency, the UNHCR, has defended its handling of the relief effort, after sharp criticism from Oxfam.

The BBC's Nigel Margerison: The UNHCR said it couldn't hope to get on top of the chaos unless it had greater support

UNHCR spokeswoman Lyndall Sachs said the agency had now deployed more staff in the refugee camps and strengthened co-ordination, with the result that the situation was now improving.

But she said western governments should give the agency more moral and financial support.

"The UNHCR must be given support, and if we are not given support by our member governments - who are in fact what we are - the UNHCR cannot carry out its important work."

Ms Sachs said governments were often acting unilaterally, occasionally giving inappropriate aid and dealing with Macedonia and Albania independently.

She urged western governments to speak with one voice through the UNHCR to get the Albanian authorities to try to stop lawlessness and mafia involvement in camps there, and to put pressure on the Macedonian authorities to more readily accept refugees.