Addressing party workers and participants of the march at Cantt Station, Hafiz Naeem said the protest movement would continue until the government withdrew the "extortion" — the term JI uses for the petroleum levy.
The politico-religious party gradually expanded its protest campaign to 42 cities across the country, while its sit-ins in provincial capitals completed 35 days on Saturday.
The party intensified its campaign in stages following five unsuccessful rounds of negotiations with the federal government, with Hafiz Naeem terming the Islamabad long march the "final call" in its campaign against the petroleum levy.
Hafiz Naeem said the party's first stop would be Hyderabad, where participants would continue their journey towards the federal capital.
"The government itself is forcing people to protest," Hafiz Naeem said, alleging that ministers came for negotiations but failed to provide relief.
He warned that if the levy was not withdrawn, the protest would intensify and could eventually turn into a movement to bring down the government.
Hafiz Naeem said JI was not travelling to Islamabad for itself or the party but for the country's 250 million people.
"We have no desire to protest in extreme heat," he said, adding that the people had been left with no other option.
He also criticised the government's role in agreements with independent power producers (IPPs), saying government representatives were present in the arrangements.
According to a JI spokesperson, the party's protest march against the petroleum levy began from Karachi today and is scheduled to receive welcomes at Hyderabad, Tando Adam, Nawabshah and Mehrabpur railway stations.
The spokesperson added Hafiz Naeem would address a public gathering in Rohri at 8pm today.
The caravan is scheduled to depart Rohri for Multan on September 21, where the JI emir will address participants at the conclusion of the train march.
Following the completion of the train march, a road caravan will leave Multan for Lahore on September 22, while the final leg of the long march from Lahore to Islamabad is scheduled to begin on September 23.
Earlier on Friday, the JI emir said the march would reach Islamabad on September 23 and 24.
He said that people would begin arriving in Islamabad from all four directions on September 20, while clarifying that the party would not block roads.
The JI chief's remarks came days after the party rejected the government's special fuel relief scheme, saying the package could not be a substitute for abolition of the petroleum levy.
He also criticised the absence of relief on diesel, saying it drives the country's economic activity.