CALCUTTA, India (AP) _ A bomb wrecked two buildings before dawn Wednesday in a congested district of India's second-largest city, reportedly killing at least 50 people and injuring about 100.

There was no immediate claim of responsibility for the explosion, which came five days after bombs in Bombay killed about 300 people. Calcutta is about 1,000 miles east of Bombay.

Police said a bomb ripped through the Bowbazar district, destroying two rickety, turn-of-the-century buildings. The two-story structures had furniture stores on the street level and storerooms above where day laborers slept.

The Press Trust of India news agency reported that the death toll had risen to at least 50 by seven hours after the 12:15 a.m. blast. Firemen continued to search for more victims.

Casualties arrived at hospitals with severed limbs and severe burns. Police said 90 to 100 people were hospitalized or treated for lesser injuries and released.

Along with the day laborers, many victims were homeless rickshaw pullers and other poor people who had been sleeping on the street outside.

''I was sleeping on the pavement and woke up from this deafening sound. We saw smoke all around us. We thought a storm had hit us,'' said Mumtajuddin Ahmed, who lives on the sidewalk about 150 yards from the explosion.

''Around midnight, I was aroused from my sleep by a huge explosion,'' said Mohan Chand Dutta, who lives near the blast site.

''I rushed outside but there was only smoke. I couldn't see anything but I could hear people screaming. There was complete chaos,'' Dutta said.

Samar Basak, another neighborhood resident, said private trucks collected the wounded and drove them to hospitals before ambulances began arriving. Volunteers were urging people to donate blood at the nearest clinic, he said.

About 10 million people live in Calcutta, a decaying city that was the capital of Britain's colonial empire in the Indian subcontinent.

On Friday, 13 bombs detonated in Bombay, India's biggest city, killing about 300 people and injuring more than 1,100. The bombings wrecked the stock exchange, offices and apartment buildings.

A militant Sikh group claimed to have set the Bombay explosions, but police said they were treating the Sikhs as only one possibility.

India recently has been wracked by Hindu-Muslim violence, including riots that killed dozens in Bowbazar and other Calcutta neighborhoods in December and January.

After the Bombay blasts, the U.S. State Department renewed its warning to Americans not to travel to India because of the ethnic tensions and violence.