More than 130,000 Afghans have fled the coronavirus outbreak convulsing Iran to return home to Afghanistan amid fears they are bringing new infections with them to the conflict-ridden and impoverished country.

The huge spike in Afghans crossing the porous border from Iran, in one of the biggest cross-border movements of the pandemic, has led to mounting fears in the humanitarian community over the potential impact of new infections carried from Iran, one of the countries worst affected by the virus.

With the Afghan ministry of health warning that some 16 million people could become infected and tens of thousands could die, experts say the wave of returning labourers and refugees, who are then dispersing throughout the country, is threatening an already complex health and security situation.

According to a joint situation report from the World Health Organization and the UN’s Office for the Coordination of Humanitarian Affairs at the weekend, while only 174 Afghans are confirmed to have the virus, the real number may be much higher because of limited ability to test and trace contacts.

For its part, the Norwegian Refugee Council warned at the end of March that “given the prevalence of Covid-19 in Iran, [the] humanitarian community’s main focus now is on provinces and districts that are considered to be at highest risk due to the volume of cross-border movement.

“This includes 25 districts that are the primary destinations for returnees from Iran, with Herat, Nimroz, Kabul, Balkh, Faryab being at the highest risk due to their greater connectivity to outbreak provinces in Iran.”

Underlining the concerns is the fact that the majority of confirmed cases are located in the western Herat province bordering Iran, a transit point for many of those crossing.

Herat province, which borders Iran, has the most confirmed Covid-19 cases. Photograph: Jalil Rezayee/EPA

At a camp on the outskirts of Herat, the Guardian met recent returnees from Iran who explained that they had fled Iran both because of fear of the virus and because the lockdown there had put them out of work.

Among them was Mirwais, 18, from Baghlan province, who had been working as a labourer for two years.

“The situation was getting worse everyday. Because of the quarantine I couldn’t work any more. Secondly, I was afraid of coronavirus,” he said.

“The border was so busy. Everyone was scared of the virus. I put up with so many humiliations in Iran to send money home. But I couldn’t resist coronavirus because I’m the only one who works in my family and if I die, they would die too, of hunger.

“Now I don’t know what to do. I don’t know whether to go home penniless or stay here. I had just enough money to get to the border.”

Zainullah, 24, from Ghazni province, who had been employed in a workshop making chairs, told a similar story.

“Most of my relatives left Iran due to coronavirus in last month. My parents insisted I come back. I did not want to return. I need 400,000 Afghanis (£4,213) to get married. I paid half of them to my fiance’s father and now he wants another half.

“Coronavirus has destroyed my life. I have no idea what to do next.”

Gul Ahmad, 43, said another factor was the lack of healthcare for Afghan workers as Iranian doctors were preoccupied with caring for Iranians. “We could not go to doctors for a very simple reason. Iranians were busy with treating their own people, they won’t give a damn for a sick Afghan.”

Eynoddin Aslami, head of the camp, said record numbers of Afghans had been arriving. “For a month there were more than 13,000 people crossing the border every day although that has decreased to around 3,000 a day.

“We are all concerned here. We are so worried about the current situation. We encounter hundreds of new arrivals every day.

Herat has been put under lockdown, along with other Afghan cities. Photograph: Anadolu Agency/Getty

“We try our best to stay away from them, but it is impossible. And some may be infected.”

Dan Tyler of the Norwegian Refugee Council echoed the concerns of many, saying: “There has been a massive spike in the number of spontaneous returns. There’s already a lockdown in Herat and around Kabul and Kandahar, and we’re really concerned about the humanitarian impact. It’s already challenging. The border on the Pakistan side is closed and we are expecting more measures.

“Supply lines are chocking up which is a real concern in a country on the brink of famine. On top of that there is the issue of the Taliban and other armed groups allowing access in areas that are not accessible, which underlines the talk there has been around a [global] corona ceasefire.”

Earlier this month Joel Millman, of the International Organization for Migration, which has been tracking the returns from Iran, warned of the danger of widespread transiting via unofficial border crossings.