More than 350,000 Afghan refugees have returned to their war-torn homeland from Pakistan this year, UN data show, with the torrent of people crossing the border expected to continue.

Earlier in October the UN's refugee agency UNHCR said the number of documented Afghan refugees returning from Pakistan had soared past 200,000.

But this week the body's Office for the Coordination of Humanitarian Affairs (OCHA) in Afghanistan released updated figures that also include the number of undocumented refugees crossing the border.

‘So far this year, 162,186 undocumented returnees and 207,236 registered returnees (369,422) have returned to Afghanistan from Pakistan,’ an OCHA statement said, noting that the majority, some 333,000 people, have returned since July.

‘If that sounds like a lot, it is,’ the statement continued.

‘Based on current trends, we expect a further 446,000 (both registered and undocumented) Afghans to arrive before year-end.’

The influx of refugees threatens to overwhelm Afghanistan, with authorities there already warning of a humanitarian crisis as hundreds of thousands of people flee fighting within the country.

‘Due to hostilities in Kunduz and intensified fighting across the south we have seen a jump of 37,000 IDPs (internally displaced people) alone -- more than 10 percent of the year total in just one week,’ Danielle Moylan, a spokeswoman for OCHA, told AFP on Monday.

The total number of IDPs due to fighting since the start of the year stands at 323,500.

- Struggling to accommodate -

For decades Pakistan has provided safe haven for millions of Afghans who fled their country after the Soviet invasion of 1979.

Pakistan hosts 1.4 million registered Afghan refugees, according to UNHCR figures from earlier this year, making it the third-largest refugee hosting nation in the world. A further one million unregistered refugees are estimated to be in the country.

Since 2009, Islamabad has repeatedly pushed back a deadline for them to return, but fears are growing that the latest cutoff date in March 2017 will be final.

A security crackdown against undocumented foreigners in Pakistan coupled with a UN decision announced in June to double cash grants for voluntary returnees to $400, has also seen a surge in returnees.

OCHA said that the vast majority of undocumented returnees claim they intend to return to the eastern province of Nangarhar. Many also settle in Kabul.

The capital already has one of the highest population growth rates in the region -- some 1,200 people every day, according to European Union ambassador Franz-Michael Mellbin -- and is struggling to accommodate the new arrivals, with many forced to shelter in informal settlements on the city's edge.

Many of the returnees to conflict-torn Afghanistan have lived in Pakistan for decades and hope to one day come back to their adopted country.

‘Inshallah, we will come here again, this time with passports,’ Mohammad Anwar told AFP last month as he prepared to leave the country he arrived in as a child and has sheltered him for 35 years.