Nearly 70,000 Afghans have returned from virus-hit Iran in the past 20 days, an official said Monday, overwhelming health workers at border crossings and raising fears of a major outbreak in the impoverished country.

They were allowed back in after Kabul reopened land crossings for Afghans wanting to return home -- despite having earlier suspended air and ground links over fears of the virus spreading from Iran, one of the world's worst-hit countries.

More health workers and better testing facilities were needed to cope with the increasing number of returnees and avoid a health disaster, warned Jawed Nadim, head of the refugees repatriation department in the western province of Herat, which borders Iran.

Health workers "only ask (returnees) some questions and test their temperature", Nadim told AFP, adding: "This is not enough." Iran has recorded 853 deaths from the new coronavirus since February 19, officials said Monday, appealing for people to stop travelling.

Afghanistan has 21 confirmed infections so far, most of them in Herat. But the official number likely understates the scale of the problem due to inadequate testing measures and shoddy health infrastructure in the war-ravaged country.

In a sign of authorities struggling to contain the disease, dozens of people fled the isolation section of a Herat hospital on Monday. They escaped "with the help of their relatives, after beating up the doctors and breaking windows," health ministry spokesman Wahidullah Mayar said, adding the police had been of "no help".

Ebrahim Mohammadi, director of the Herat ambulance service, said 37 people had absconded. Two had tested positive for the COVID-19 illness while results were pending for the rest. "They were getting impatient because after more than five days their test results still hadn't come," Mohammadi told AFP.

Returnees more than double

Many Afghans who had gone to Iran to look for work are returning home as the contagion cripples Iran's economy, which was already devastated by US sanctions. Afghanistan's spring harvest is also drawing workers home, said the International Organization for Migration.

The number of returnees jumped by 106 percent at two border crossings in the first week of March from the previous week, its figures show. Ninety percent of those returnees came home voluntarily, while the remaining 10 percent were deported, it added.

Herat's governor Abdul Qayum Rahimi last week said Afghanistan needed to act quickly to avoid a spiralling crisis.

"With the number of people coming in from Iran (and) entering Afghanistan from several entry points if we don't take any measures now and don't work together... we will witness an even worse situation than Iran," Rahimi said Saturday. "I am afraid... (that) a day will come that we won't be able to count the dead bodies," he said.

Returnees told AFP they were tested for coronavirus symptoms -- mainly fever -- at the border crossing. "The doctors at the border use thermometers to test (for) fever and... are advising us how to protect ourselves from coronavirus", said Malik, a 46-year-old labourer.

Public Health Minister Ferozuddin Feroz announced Monday the government would build a 300-bed facility in Herat to tackle the outbreak. "With that, the capacity of the health facilities in Herat will increase to 1,000 beds," he said.