The international cricket star-turned-politician plans on Wednesday to lead tens of thousands of people from his power base in the northwestern city of Peshawar to the capital demanding fresh elections — in a centre-piece showdown with his rivals.
In Lahore, police deployed tear gas against Khan supporters attempting to remove roadblocks and travel to Islamabad in convoys.
"Nobody should be allowed to besiege the capital and dictate his terms," interior minister Rana Sanaullah said Tuesday.
Police crack down on protesters of the Pakistan Tehreek-e-Insaf (PTI) party in Lahore on Wednesday. AFP
Schools in Islamabad and neighbouring Rawalpindi were closed and all exams cancelled, while a state of emergency was declared at all hospitals, with staff put on alert.
"We have seen the capital blocked before but this is something unprecedented," Islamabad private school worker Allah Ditta, 52, told AFP.
Salon worker Sawera Masih complained that the wide-scale disruption was falling hardest on daily wage workers like herself.
"Whoever is in power doesn't make a difference to us, but not earning even for a single day affects me and my family," the 23-year-old said.
The coalition government headed by Prime Minister Shehbaz Sharif has pledged to stop Khan's supporters from pouring into the city, calling the rally an attempt to "divide the nation and promote chaos".
Police officers assemble next to shipping containers placed by authorities to block a road in Islamabad, Pakistan. AP
"Nobody should be allowed to besiege the capital and dictate his terms," interior minister Rana Sanaullah said on Tuesday.
Entry and exit points on key highways that lead to the capital were blocked by police around the nearest main cities of Peshawar, Lahore, and Multan.
Islamabad police on Wednesday published a traffic plan showing a complete blockade of the city and a heavy security presence.
On Tuesday, Khan's Pakistan Tehreek-e-Insaf (PTI) accused police of arresting and detaining hundreds of its supporters in overnight raids.
Police sources in Lahore who asked not to be named told AFP more than 200 supporters were detained on public order offences.
Shipping containers placed by authorities block a road in an attempt to foil a planned rally, in Islamabad. AP
The government and police have said that protestors had been planning to join the march with weapons.
One police officer was shot dead during the raids, Punjab Chief Minister Hamza Shahbaz Sharif said.
But a defiant Khan told reporters in Peshawar he would lead the largest march in Pakistan's history.
"I don't consider it politics but jihad," Khan said, referring to a term used by Muslims to describe a struggle.
In 2018, Khan was voted in by an electorate weary of the dynastic politics of the country's two major parties.
The popular former sports star had promised to sweep away decades of entrenched corruption and cronyism but is believed to have fallen out with Pakistan's generals.
He was brought down in part by his reported failure to rectify the country's dire economic situation, including its crippling debt, shrinking foreign currency reserves and soaring inflation.