He said the government should understand that the PTI movement would not stop until Sharif resigned, Dawn online reported.
"I am ready to sit with the protesters at the sit-in for one year but will not leave the place without the prime minister's resignation," Imran Khan said.
He said the government was afraid of the ideology of the participants of the sit-in. He appealed to the PTI supporters across the country to reach Islamabad and participate in what he called the historical sit-in.
"Nawaz Sharif, if you try to arrest my supporters I will not spare you," Pakistan Awami Tehreek (PAT) chief Tahirul Qadri said.
Qadri added that he would lead his supporters in the fight against police if the government tried to arrest PAT workers.
The protests led by Imran Khan and Qadri began Aug 15 in an attempt to overthrow Prime Minister Nawaz Sharif, whom they have accused of rigging the 2013 general election.