A bomb ripped through a packed movie theater in northern India on Sunday, killing at least six people and wounding more than 30 others at the start of India's festival season, a time of year marked by major Muslim and Hindu holidays, authorities said.

The blast at the Shringar Cinema in Ludhiana, an industrial town in Punjab state, was the second apparent terror attack this week in northern India, coming days after two people were killed in the bombing of a venerated Muslim shrine in the neighboring state of Rajasthan.

Sunday's attack took place on one of the holiest days of the Muslim calendar, Eid al-Fitr, which marks the end of the holy month of Ramadan, and came weeks before two major Hindu festivals, Dussehra and Diwali.

The cinema was packed when the blast occurred around 8:50 p.m. (1520 GMT) in one of its three theaters where some 600 movie-goers were taking in a recently released Bollywood romance, "Janan Janam Ke Saath," or "Together Through Several Lifetimes," the Press Trust of India news agency reported.

India television broadcast scenes of shattered windows and glass doors in the cinema's lobby, and the CNN-IBN television news channel said some of the wounded had lost limbs in the blast.

A senior police official, Ishwar Singh, told reporters that the explosion was caused by a single bomb and that six men had been killed — two who died in the blast and four who later succumbed to their injuries.

At least 30 others were being treated for wounds sustained in the attack, he said. Other officials warned that the death toll could rise.

Sunday's explosion drew immediate comparisons with the bombing earlier this week at the shrine of a 12th century Sufi saint, Khwaja Moinuddin Chishti, although officials offered no evidence of a link.

Authorities say Thursday's explosion, which took place in the town of Ajmer, was caused by a small bomb packed inside a tin lunch box that was detonated during evening Muslim prayers. Police also discovered another bomb at the shrine that had apparently failed to detonate.

No one has claimed responsibility for either attack. But investigators say they have interrogated Indian and Bangladeshi pilgrims in connection with the bombing of the Muslim shrine, although they have so far made no arrests.

India has routinely blamed Pakistani and Bangladeshi-based Islamic militants for a series of attacks that have rocked the country over the last two years, including several at mosques, saying they were trying to provoke violence between India's Hindu majority and Muslim minority. However, little concrete proof has been provided in the past.

Relations between Hindus, who make up more than 80 percent of India's population, and Muslims, who account for about 130 million of India's 1.1 billion people, have been relatively peaceful since the bloody partition of the subcontinent into India and Muslim Pakistan at independence from Britain in 1947. But there have been sporadic bouts of violence.