A trickle of refugees made it across the border from Greece into Macedonia on Friday hours after police had fired stun grenades at the crowd, injuring at least five people.

Tensions have been rising since Thursday when Macedonia declared a "state of emergency"and sealed its border with Greece as thousands have been crossing on their way to Serbia and onward to EU-member Hungary.

After several hours of clashesbetween police backed by armored vehicles against the increasingly desperate crowd of refugees - most of them Syrians - several hundred managed to break through and cross the frontier, the Reuters news agency reported.

"The police moved away and we entered, no one stopped us," one refugee told Reuters, without giving his name

UNHCR appeals to Skopje to reopen border

The UN has criticized Macedonia's decision to seal the border near Gevgelija, about 120 kilometers (75 miles) from the capital Skopje, which has left thousands of men, women and children stuck in no-man's land as aid workers struggle to render assistance.

"These are refugees in search of protection and must not be stopped from doing so," said UNHCR chief spokeswoman Melissa Fleming.

UNHCR chief Antonia Guterres said Friday that he had spoken to the Macedonian foreign ministry and received assurances that the border will not remain closed.

He also called on authorities in Greece to provide urgent assistance to "people stranded on the Greek side of the border" and to help them move towards refugee reception facilities further from the border zone, Reuters reported.

Fleming also urged Europe to find a solution, saying that Macedonia and Serbia "cannot be left alone with this number of refugees."

Migrants on the border say they fear being sent back to Greece where local authorities are overwhelmed by the influx of roughly 160,000 migrants who arrived at its shores so far this year, often in small holiday resorts on islands like Kos and Lesbos not equipped to deal with the situation.

"We don't want to go back, we are very exhausted from walking," a biology student waiting at the Macedonia-Greece border, who asked not to be named, told the AFP news agency.

"We are exhausted from the situation in Syria. My father died from a [bomb]shell. I had to leave, I have no one there any more. I want to continue my education in some other country, I don't want to go back to Syria," he said.

Macedonia says 'vulnerable' may pass

Macedonia's interior ministry says it would begin allowing a number of "vulnerable" refugees to begin crossing but did not disclose how it would determine who would be singled-out for special treatment.

"A limited number of illegal migrants in vulnerable categories are allowed to enter Macedonia and they may be provided aid in accordance with the state's capacities," the Interior Ministry said in a statement, AFP reported.

Police say they have issued temporary transit documents allowing 181 migrants to exit in the past 24 hours. The refugees were mostly from Syria, Bangladesh and Pakistan, the statement said.

Before the border was sealed it had been issuing an average of 1,300 such documents a day, it added.

More than 41,000 migrants have been processed by police crossing the border into Serbia since June 19.

jar/kms (AFP, Reuters, dpa)