In one of the incidents, at least two people were killed and 25 suffered injuries when two successive blasts struck near an office of the MQM, a political party.
The first blast was reported to be a cracker attack on a Fiqah-e-Jafria mosque, located near the MQM office, the second one, according to sources, was an improvised explosive device.
The country's caretaker Prime Minister Mir Hazar Khan Khoso condemned the attack, while asking the concerned authorities to take action against the culprits, Xinhua reported.
MQM chief Altaf Hussain, who is in self-exile in Britain, condemned the incident while urged the government to take immediate action against those responsible for the attack.
At the time of blast the office was closed and no party worker was hurt in the attack, said MQM leader Wasay Jalil.
No group or militant organisation immediately claimed responsibility for the attack.
In a separate incident, two people, including a minor girl, were killed and 19 injured when a blast occurred near Pakistan Peoples Party (PPP) corner meeting in the city's Lyari town Saturday night, Geo News reported.
The bomb was hidden inside an motorcycle, police said. It was a remote-controlled blast, police sources added.