It is now 48 hours since any refugees emerged from the deep gully on the Serbian side of the border. And the disappearance of some 25,000 refugees known to have been on the road south is mystifying senior aid agency officials.
For the past 45 days this border post - and the wide valley of the River Lepenec - has been the scene of some of the most appalling sights in the great exodus of Kosovo Albanians. Each day they have streamed out without pause - never fewer than 6,000 a day, the numbers sometimes approaching 20,000.
Now, like a river that has suddenly evaporated, it has stopped completely. And on the floor of the valley - where six weeks ago over 100,000 trapped people came close to starving before the eyes of the world's media - not a figure is seen.
"It is becoming clear that something very bad is happening up there," said Paula Ghedini of the UNHCR. "We know for sure that the Serbs have been carrying out large-scale clearance operations on some fresh regions to the west of Pristina. We have accounts of villages burning and tens of thousands of people being forced up into the hills.
"So where are these people? Why are they not being sent down by train as they have been for weeks? They are either living rough and perhaps starving on the hills, or they are being rounded up and held for a purpose we are not sure of. Either way, it is very frightening."
From the high hills overlooking the Macedonian side of the border the road that winds down from Pristina can be seen. For over six weeks it has been packed with vehicles, but now it is empty.
And down by the river the railway track that forms the main line from Pristina and Skopje is silent. Hundreds of trains have delivered the refugees into no-man's land on this line. No trains have been seen for nearly 60 hours.
Aid workers, soldiers and border guards waited patiently beside the 50 or so holding tents that have been put up.
But as night began to fall it became clear that we were witnessing a big change of Serb tactics. Somewhere, hidden from view among the dark hills, tens of thousands of people are being held for a purpose that nobody can guess.