Afghanistan's capital has become an unlikely pandemic transit route for Pakistanis desperate to reach the riches of Saudi Arabia despite deteriorating security and the threat of bomb blasts.

With most Gulf flights from Pakistan cancelled as the country is added to a growing number of coronavirus travel blacklists, thousands of workers are hoping to reach the kingdom after first spending two weeks in Kabul.

"I'm a little bit worried," said Sohaib Siddiqui, a 31-year-old electrical engineer from Lahore, in line at the Afghanistan embassy in Islamabad.

But he added that he was "willing to take risks", explaining that a job in Saudi Arabia would allow him to send between 50,000 and 100,000 rupees ($325-$650) a month to his family of three.

The Gulf countries have long been a vital avenue of employment for Pakistanis, who send back billions of dollars in remittances every year, propping up the cash-strapped economy. 

In the past month alone, tens of thousands of Pakistanis have applied for transit visas at the Afghan embassy in Islamabad, according to an official at the mission.

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Over the past week, hundreds have camped overnight to submit their paperwork.

The plan is not foolproof, however, with the one direct flight between Afghanistan and Saudi Arabia cancelled in recent days, according to a travel agent in Kabul.

Special flights were available only to workers who already had Saudi residency -- at a cost of around $1,300.

- Travel woes -

The influx of travellers into Kabul comes as US troops are pulling out of the country following nearly 20 years of war, with violence surging.

Large swathes of the population in Kabul also nurture a seething hatred for their Pakistani neighbours, with authorities there long blamed for supporting the Taliban insurgency.

"We have no choice, what should we do?" said Tanweer Ahmad while waiting in line in Islamabad to file his application for an Afghan visa. 

At a diagnostic centre in Kabul, doctors have been mobbed with Pakistanis desperate for the Covid-19 tests needed to enter Saudi Arabia, doubling demand at the lab in recent weeks.

"Saudis and the Pakistanis trust Afghan laboratories," beamed Sediqqullah Safi, a doctor at the testing centre, saying he hoped the new batch of visitors would inject much-needed money into the capital's slumping economy.

"They come here with benefits -- they're spending money on shopping, transportation, and of course on coronavirus tests."

For Anwar Khan --- who spent two weeks in the capital and is hoping to fly to Saudi Arabia soon -- the unnerving trip has been worth it. 

"One would of course worry about security," said Khan. "Thank God there has been no problem (for) us so far."

For those still hoping to make it to Afghanistan -- where virus cases are also rising following the Muslim holiday of Eid al-Fitr -- any future change in the rules might make the trip impossible, or leave them stranded in Kabul after exhausting their savings.

"I have small kids at home and no other source of income," said Liaquat Ali.

"We are taking a big risk going to Afghanistan. There are no guarantees."