At least 25 people died in the state capital of Gauhati in one of several blasts across India's northeastern state of Assam on Thursday. (Anupam Nath/Associated Press)

At least 68 people are dead and scores more wounded after a string of 11 bomb attacks ripped through India's northeastern state of Assam on Thursday, police said.

At least 36 people died as a result of four blasts in the state capital of Gauhati, while the remaining 32 were killed in three other towns in the state, a spokesman from Assam's chief minister office said. Security analysts believed the blasts were co-ordinated.

Police said more than 335 people were wounded in the blasts.

It was not known who was responsible for attacks, but the area is a hotbed of militant separatist activity. Assam has also recently been subject to bomb blasts blamed on Bangladeshi Islamic militants, a group that one expert linked to Thursday's attacks.

"These blasts look like the handiwork of terrorist groups from Bangladesh, as you need sophisticated militant groups to carry out such co-ordinated attacks," Maj.-Gen. Ashok Mehta, a security analyst, told Reuters in New Delhi.

"It is quite possible that separatist groups are not involved at all."

Police were searching for more unexploded bombs.

Went off in crowded areas

Many of the bombs were detonated near crowded areas, and one explosion took place a few hundred metres from the secretariat in Gauhati, the building that houses the offices of the chief minister, the state's top elected official.

"I was shopping near the secretariat when I heard three to four loud explosions. Window panes in the shops shattered and we fell to the ground as the building started shaking," H.K. Dutt, who was lightly wounded by shrapnel, told the Associated Press.

"I stood up and saw fire and smoke billowing out, then I looked down and saw blood on my shirt and realized I had been injured," Dutt said.

The bombings in Gauhati sparked riots as people took to the streets in anger. People stoned vehicles and torched at least two fire trucks, the Associated Press reported. A curfew was imposed on the city.

The area is an isolated region wedged between Bangladesh, Bhutan, China and Burma with only a thin corridor connecting it to the rest of India.

More than 10,000 people have died in separatist violence over the past decade in the region.

With files from the Associated Press, Reuters