The largest bomb exploded near the secretariat - the office of the Assam state's top government official - leaving bodies and mangled cars and motorcycles strewn across the road. Bystanders dragged the wounded and dead to cars that took them to hospitals.
Police officers covered the burned remains of the dead with white sheets, leaving them in the street.
No one claimed responsibility for the blasts that went off within minutes of each other, but dozens of militant separatist groups have been fighting the government and one another for years in the region.
"I was shopping near the secretariat when I heard three to four loud explosions. Windowpanes in the shops shattered and we fell to the ground as the building started shaking," said H.K. Dutt, who was lightly wounded by shrapnel.
"I stood up and saw fire and smoke billowing out, then I looked down and saw blood on my shirt," Dutt said.
N.I. Hussain, Gauhati's deputy inspector general of police, told the CNN-IBN news channel that police in the state were on high alert and searching for more unexploded bombs. "There may be more blasts. You never know," he said.
Later, dozens of people angry over the blasts took to the streets of the state capital, stoning vehicles and torching at least two fire engines. Police imposed a curfew on the city and shut down roads leading in and out of the area.
U.S. Ambassador David Mulford condemned the attack.
"Americans share their sorrow and outrage at these horrific attacks on innocent people," he said.
The isolated region wedged between Bangladesh, Bhutan, China and Myanmar with only a thin corridor connecting it to the rest of India is a hotbed for separatists who accuse the central government of exploiting the region's natural resources while doing little for the indigenous people - most of whom are ethnically closer to Burma and China than to the rest of India.
More than 10,000 people have died in separatist violence over the past decade in the region.
The area also has been hit recently by ethnic clashes. At least 49 people were killed in July in violence between members of the native Bodo tribe and recent migrants to the area, most of whom are Muslims.
The government has blamed several previous serial attacks in India on Islamic militants from nearby Bangladesh.
