Pakistani authorities began rounding up undocumented foreigners, most of them Afghans, on Wednesday, ahead of a midnight deadline for them to leave or face expulsion.

The removal of people to temporary holding centres began a day earlier than previously announced. The interior ministry said 140,322 people had already voluntarily left after days in which trucks piled high with belongings and crammed with people have jammed major roads out of the country.

Pakistan set the Nov. 1 start date last month for the expulsion of all undocumented immigrants, including hundreds of thousands of Afghans. It cited security reasons, brushing off calls to reconsider from the United Nations, rights groups and Western embassies.

Some of those ordered to leave have spent decades in Pakistan.

"A process to arrest the foreigners... for deportation has started as of Nov.1," the interior ministry said in a statement, while adding that voluntary return would still be encouraged.

Within hours of the interior ministry statement, authorities had begun detaining and transferring what they said were undocumented foreigners to transit centres.

Afghan refugees with their belongings arrive on trucks from Pakistan at the Torkham border. AFP

In the southern port city of Karachi, home to a large number of Afghan migrants and refugees, deputy commissioner Junaid Iqbal Khan said up to 74 people had so far been moved to one of the transit centres, up to 40 of them without any proper documents.

Reuters witnesses saw police bring some people in police vehicles. Inside the centre, authorities had set up tents to shelter those rounded up. Media were not allowed access inside.

Most of the Afghan nationals were brought to the centers in rickety busses, some of them handcuffed.

Some complained about mishandling by the authorities.

Jan Muhammad, 40, said his cousin was detained even though he had all the legal documents.

"I have shown up here with his original card," he told Reuters, saying the guards were now asking for another document. "We didn't bring that with us."

Afghans head home

Of the voluntary returnees, around 104,000 Afghan nationals have left the country via the main Torkham border crossing in northwest Pakistan during the last two weeks.

"Some of them have been living in Pakistan for more than 30 years without any proof of registration," said Nasir Khan, the area deputy commissioner.

Another 35,000 Afghan nationals who didn't have legal documents to stay returned voluntarily by the Chaman border crossing in the southwestern province of Balochistan, provincial caretaker minister Jan Achakzai said. About 100 such Afghan nationals were arrested, he said.

Local media pictures showed long queues of busses heading to the Torkham crossing where thousands of people waited for clearance and would likely spend night in open as the crossing closes at 9pm.

Some of them said they had never been to Afghanistan, and wondered how would they start a new life there.

Afghan refugees arrive at a holding centre before their departure to Afghanistan near border in Chaman. AFP

"We have never been to Afghanistan," Rizwan Khan, 25, told Reuters in Khyber tribal district before heading to the border. "We would be strangers to the people and they would be unknown to us. We do not have a house to live in in our native village," he said.

His grandfather had migrated from Afghanistan.

Of the more than 4 million Afghans living in Pakistan, the government estimates 1.7 million are undocumented.

Many fled Afghanistan during its decades of internal conflict since the late 1970s, while the Taliban takeover after the US withdrawal in 2021 led to another exodus.

Pakistan has taken a hardline stance, saying Afghan nationals have been behind militant attacks, smuggling and other crimes in the South Asian nation.

Kabul has dismissed the accusations.

In the Afghan capital, the Taliban administration asked all countries hosting Afghan refugees to give them more time to prepare for repatriation.

"We call on them not to deport forcefully Afghans without preparation, rather give them enough time and countries should use tolerance," it said in a social media posting on Afghans in Pakistan and elsewhere.

It assured Afghans leaving over political concerns that they could return and live peacefully in Afghanistan.

Reuters