The MQM chief took back his decision hours after announcing his resignation in a telephonic address to party leadership.
Tehreek-i-Taliban Pakistan claims responsibility for the attack.
Party says worker killed; schools, business centers and petrol stations shut down as activists protest raid.
Police investigation into the incidents is under way.
Suspect allegedly admits to killing more than nine people, including police officials.
Counter Assault Teams comprising police commandos will be formed to deal with emergency situations in the province.
The fire has burned furniture worth hundreds of thousand rupees to ashes.
The police team will bring the alleged Lyari gang leader back to Karachi for further judicial process.
Baloch was travelling from Muscat to Dubai, when the arrest took place.
A grenade attack that injured 20 people at an MQM camp, lead to the death of one critically injured worker.
South Zone’s Special Investigation Department carried out raids in Korangi and arrested Mazhar.
The police has requested the suspension of mobile phone services in other parts of Sindh as well.
Prime Minister Nawaz Sharif has approved the appointment of Ghulam Haider Jamali.
The suspects were arrested during a joint search operation carried out by Rangers and police personnel.
The bomb contained 10 kilograms of explosives and was planted in a box outside a marble factory.
The officer was shot near Tibet Centre on M A Jinnah Road while he was travelling towards the city's Civic Centre.