The explosion at a hotel in Hub, an industrial town some 600 kilometers south of Quetta, injured six others, police official Ghulam Ali Lashari told AFP.
Thousands of people attended funeral prayers for Nawab Akbar Bugti on Tuesday, police and witnesses said.
The crowd gathered at a sports stadium in memory of Bugti, who was killed in a military operation on Saturday. Police contingents ringed the stadium in the provincial capital of Quetta and troops were standing by on alert, witnesses said.
"It is a big tragedy. Bugti has become a legend," 22-year-old clan member Dad Mohammad told AFP. "He fought for the rights of ethnic Baloch. He had set a course for the Balochis-it is now up to the people," said another tribesman, Slaim Shahwani, 25.
The city was tense and shops were closed in mourning. Traffic was thin as a heavy police presence patrolled main roads and security was beefed up at government installations. "The authorities have made elaborate arrangements for protecting the lives and property of the people," provincial government spokesman Raziq Bugti told state media.
Mourners coming are groups included tribal elders, ex-ministers and former provincial governors. Bugti's son-in-law Senator Agha Shahid said that the family approached the ruling party for help in getting the body but that so far there had been no response.
A crowd firing weapons into the air had rampaged through the streets of Quetta following funeral prayers.
The mob torched a local bank and set a district government building alight, setting off plumes of thick black smoke, an AFP reporter said. Four makeshift bombs exploded in shops near the venue of the prayers.
Police fired tear gas as well as rounds in the air to try to bring the situation under control, police official Abdul Khan said. Paramilitary troops were brought in to quell the violence.
Security forces exchanged fire with gunmen after the prayers and one policeman was killed, police said. Police said about 10,000 people attended prayers for Bugti in Quetta. At the end, some mourners threw stones at police and set fire to government offices, shops and vehicles. Firing soon erupted, a witness said.
"Some protesters have taken positions on rooftops and they are firing at the security forces," said the witness. Provincial police chief Chaudhry Mohammad Yaqub told Geo television that one policemen had been shot dead and one wounded. A shop-keeper was also wounded, a hospital doctor said.
"There is a lot of agitation. They're destroying public property. We're are trying to hold our ground," deputy provincial police chief Salman Saeed told Reuters earlier.
Rioting also erupted in the port city of Gwadar and several other areas, police said. The protesters have attacked government offices, vehicles and homes and shops of people from outside the province.
It was the third consecutive day of unrest in the area, which has led to more than 500 people being arrested and two killed. Baloch nationalists also called a general strike in protest.
Violence was also reported in several other areas in Balochistan, including in the coastal town of Turbat where protesters were said to have torched three shops and one bank. Bugti, who was in his 80s, was a tough and controversial figure, an Oxford-educated powerbroker who dominated Baloch politics for decades.
His body has not yet been recovered from the cave, which collapsed during a heavy exchange of fire between security forces and his armed men, officials said.
Pakistan military spokesman major general Shaukat Sultan told a press conference in Rawalpindi, that it would take another four or five days to retrieve the body of Bugti from the rubble. Sultan said it was not clear what caused the blast and denied that Bugti was the target of the strike.
"Our basic purpose is to retrieve the bodies from the cave," Sultan said. Troops found two boxes in rubble, which contained 100 million rupees (60 million dollars) and 96,000 dollars, some cheque books and a Thuraya satellite phone, Sultan said.
Former premier Benazir Bhutto called it a blow to the unity and integrity of the province. "His killing would further alienate the people of Balochistan from the Centre (Islamabad)," she said in a statement from London. She called for an end to military operations in Balochistan.
Separatist sentiment has been bubbling in Balochistan ever since the founding of Pakistan nearly 60 years ago, and Prime Minister Shaukat Aziz said on Monday that the military had not deliberately targeted Bugti. But President Musharraf warned that his government would crush the insurgency.
Suspected rebels blew up gas pipeline and electricity pylons on Monday. The attacks appeared to be the first by the rebels since Nawab Akbar Khan Bugti was killed in a government assault. The attackers used high explosives to blow up the pipeline and power pylons outside the city of Qalat, cutting its gas and power supplies.
"These were strong explosions. A 12-foot (3.6-metre) long piece of the pipeline was blown away," said a police officer in the city. Repair work on the gas and electricity lines had started, said the officer, who declined to be identified.