Islamabad: The opposition parties in Pakistan have started their march towards Islamabad in an attempt to counter a planned rally by the ruling Pakistan Tehreek-e-Insaf (PTI), with Pakistan Muslim League-Nawaz workers leaving from Lahore and Jamiat-e-Ulema Islam-Fazl activists starting from Dera Ismail Khan, Samaa TV reported.

The PTI, meanwhile, is preparing Islamabad's Parade Ground for its grand rally on Sunday, with thousands of its supporters having left for Islamabad.

Pakistan Information Minister Fawad Chaudhry claimed that tens of thousands of PTI supporters are already on their way to Islamabad.

The presence of a large number of rival political workers and a possibility of a showdown between them has sparked concerns among Islamabad authorities, who have declared an emergency at Islamabad hospitals while hospitals in Rawalpindi have also been put on alert, Samaa TV reported.

The capital city administration has decided to seal the red zone besides issuing a traffic plan.

The Pakistan Peoples Party, meanwhile, has advised the Opposition against holding rallies in Islamabad, saying a clash would allow Imran Khan political "martyrdom".

The PML-N's march is led by Maryam Nawaz Sharif and Hamza Shehbaz Sharif and is scheduled to arrive in Gujranwala on Saturday night. A large number of PML-N workers gathered in Lahore's Model Town on Saturday afternoon, before leaving for Islamabad using the Grand Trunk (GT) Road.