Some 80 others were wounded in the blasts, which ripped through a packed street restaurant and an amusement park auditorium, where hundreds were watching a sound-and-light show.
Police say 19 unexploded devices -- fitted with timers and placed in plastic bags -- have since been recovered at road junctions, cinema halls, pedestrian bridges, and bus stops throughout the mixed Hindu-Muslim city.
Local resident Raghav called it sad and said "It is not safe at all. [It's believed] 60 to 70 people were killed. The government is not doing anything. We don't know what will happen the next moment." Raghav said, "We are even scared to leave our homes."
Y.S. Rajasekhara Reddy, the chief minister for Andhra Pradesh state, where Hyderabad is located, said the dead include both Hindus and Muslims.
He also said available information points to the involvement of terrorist organizations based in neighboring Pakistan and Bangladesh.
No one has claimed responsibility for the attacks, but local media reports, quoting unnamed security officials, point to a possible link to the Bangladesh-based Harkat-ul-Jehad-i-Islami.
The group is believed to be responsible for the blasts at a Hyderabad mosque in May, in which at least nine people were killed. Another five died as angry mobs clashed with the police after the attacks.
Muslim leaders have said they do not trust local police to handle the investigation into the mosque attack.
Hyderabad has a history of sectarian violence between Hindus and Muslims.
In that context, Y.S. Rajasekhara Reddy appealed for calm, saying: "Don't spread rumors. In an emergency, it is the responsibility of every citizen to cooperate."
Special security measures have been made for more than 30,000 weddings scheduled to take place across Andhra Pradesh state today, an auspicious day on the local calendar.
Security has also been tightened in the national capital, Delhi, the financial hub, Mumbai, and other major cities.
India has been hit by a series of bombings in the past two years. Nearly all of them have been blamed on Islamic extremists with foreign connections.
In July 2006, bombs in seven Mumbai commuter trains killed more than 200 people. That attack was blamed on Pakistan-based Muslim militants.