A curfew was imposed in the provincial capital, Quetta, after hundreds of students rioted at news of the killing.
Nawab Akbar Bugti, 79, was killed in a gun battle near his mountain cave hideout, officials said.
He was a key figure in the struggle for greater political autonomy and share of Balochistan's gas and mineral wealth.
His death represents a major victory for the government in its campaign to undermine rebels in Balochistan, the BBC's Dan Isaacs in Pakistan says.
As news of his death spread, several hundred students from the state-run Balochistan university took to the streets in protest.
Police had to fire into the air to disperse the rioters who attacked and set fire to cars and smashed windows.
Army troops have moved in and are taking positions to enforce a curfew imposed at 0600 (0100 GMT), senior police official Zahid Afaq said.
"At the moment, the curfew is only in Quetta but if there is any law and order situation elsewhere, it will be imposed there too," he was quoted by Reuters news agency as saying.
The battle between tribal militants and government forces reportedly took place near the town of Dera Bugti.
At least 24 militants and a similar number of soldiers died in the fighting, officials say.
Pakistani ground forces backed up by helicopter gunships are said to have swooped on a cave complex on the border of Dera Bugti and Kohlu districts on Friday. Heavy fighting followed.
Information Minister Mohammad Ali Durrani confirmed to Reuters news agency that Nawab Akbar Bugti had been killed, although there is no official confirmation that the rebel leader's body has been found.
Balochistan is Pakistan's biggest province, and is said to be the richest in mineral resources. It is a major supplier of natural gas to the country.
But for decades, Baloch nationalists have accused the central government in Islamabad of depriving the province of its due.
Nawab Akbar Bugti - known to many as the Tiger of Balochistan - played a major role in the politics of the province for more than five decades, the BBC's Steve Jackson writes.
Sometimes he pursued his nationalist agenda from positions of authority and sometimes as a rebel leader.
He was involved in earlier failed insurgencies in the 1950s, '60s and '70s but he also served in the federal government and was on occasion governor and chief minister of Balochistan.
The latest fighting between government forces and Mr Bugti's followers began after attacks by separatists on the gas infrastructure in the region.
In one of his last interviews - with the BBC's Urdu Service in July this year - Mr Bugti was asked why a peace deal between his tribes and the government had not been implemented.
"They say that I am intransigent, I don't listen to them, I don't bow before them," he said.
"They say that I should bow before them and salute them, and give up my weapons, and then everything will be all right."
His vision for Balochistan has never been achieved but the insurgency he led has been one of the biggest headaches for President Pervez Musharraf in recent years, our reporter writes.
The main question now is whether or not his death will provoke more violence from the separatists, he adds.
Source:BBCGüncelleme Tarihi: 20 Eylül 2018, 18:16