The string of 16 bombings ripped through crowded places in the tinderbox city, which was the scene of deadly Hindu-Muslim riots in 2002, with targets including markets, buses and hospitals struggling to treat the victims.
Indian television channels said a little-known Islamist group calling itself the "Indian Mujahedeen" had claimed responsibility for the attacks, which came a day after a similar wave of bombings in the southern tech city of Bangalore.
Indian President Pratibha Patil expressed her "grief and sorrow" and also "appealed to the people of Ahmedabad to maintain peace and harmony," her office said in a statement.
Many of the victims had been peppered with red-hot nuts, bolts and ball bearings packed into bombs that were clearly designed to cause maximum casualties, doctors said.
At Ahmedabad's civil hospital, one of two medical facilities that were hit, victims could be seen writhing on the floor, their bodies punctured by flying pellets, and crying for treatment from overstretched and panicked staff.
All the bombs were detonated with timer devices and all went off in the space of 36 minutes, officials said.
"We should not allow anybody to make use of this blast to create more terror and to create more difficulties for the people," said India's Home Minister Shivraj Patil, also urging calm in the communally-tense state.
Gujarat's right-wing Hindu leader Narendra Modi, however, warned he "shall not spare" the culprits.
"The land of Mahatma Gandhi has been bloodied by terrorists whom we shall not spare," said Modi, the firebrand chief minister of Gujarat state - the birthplace of India's independence hero.
"Terrorists are waging a war against India. We should be prepared for a long battle against terrorism."
State leader Modi is a highly controversial figure in India - and is still accused of turning a blind eye to the 2002 Hindu-Muslim riots which left 2,000 people, mostly Muslims, dead.
Ahmedabad, however, was largely calm on Sunday morning, with large numbers of police and paramilitaries mobilised.
Major Indian cities have been hit by a string of apparently well-planned bomb attacks in recent years, with officials in the capital regularly pointing the finger at arch-rival Pakistan or militants backed by Islamabad.
Pakistan denies backing Muslim militants, including those operating in the disputed Himalayan state of Kashmir.
But earlier in the week India said the two countries' peace process was "under stress," repeating allegations that "elements" in Islamabad were behind an upsurge in militant activities including this month's suicide attack against its Kabul embassy.