MUMBAI, India — Scores of people were feared trapped or dead after a five-story residential building collapsed early Friday morning, the fifth deadly collapse this year in and around Mumbai, a city with crumbling housing infrastructure and poor building standards. At least 11 people were confirmed dead.

The authorities said it was too early to determine the exact cause of the collapse or the number of people trapped or dead inside the structure, the Babu Genu Market building. Onlookers said the building had more than 100 residents, nearly all of whom were probably home when the structure fell. The building was about 30 years old, officials said.

The scene Friday was a chaotic pile of broken steel and concrete rubble, with more than two dozen fire trucks and at least 15 ambulances on the streets.

“The building collapsed suddenly at 6 a.m. this morning,” said Tanaji Ghodge, a deputy police commissioner. “We don’t know how many people will come out of the rubble yet. The rescue operation is going on in full force.”

Babu Gupta, a sound engineer who lives next door, said the building had about 24 occupied one-room apartments, each with four to eight residents, underscoring the dangerous overcrowding in many buildings in Mumbai.

“There were many people in that building whom I was friends with,” Mr. Gupta said. “We often played cricket together on this street. There is Parmar, there is Jadhav, there are so many others. There must be at least 15 of my friends in that building. There is no news of them yet.”

Murli Khadpekar, a neighbor, said he heard a “loud bang” at 5:53 a.m. and came running out to see that the building’s huge rooftop water tank had come crashing down, and that the building had collapsed. The building was mostly occupied by city trash collectors and laborers, he said.

Hundreds of police officers, firefighters, dockyard workers and neighbors crowded around the site of the collapse Friday in the kind of chaotic scramble that is routine after such disasters in India. Police officials tried to clear the area of bystanders. Neighbors watched from balconies and terraces overlooking the spot of the collapse.

Dr. Habbu Jadav, the superintendent of a nearby hospital, said that 25 people had been brought in with injuries as of 8 p.m. Friday and that there were 11 deaths. Family members surrounded hospital officials asking if their relatives were among the dead or injured. Among them was Akhilesh Shinghade, a Mumbai city official who was pacing the hospital waiting area hoping for news of his wife, who is eight months pregnant and had been staying in the collapsed building with her parents.

He said there had been five people in the house: his wife, Namita, and her grandmother, parents and sister. “None of them have been found as yet,” he said.

Deepteesh Kadam, 16, was admitted to the hospital with a fractured left clavicle after he shimmied out of the building through a small gap. He had been sleeping in his family’s third-floor apartment when the building fell.

“I got out, but I could not find my brother,” he said.

In April, an illegally constructed building in a Mumbai suburb collapsed and killed 74 people, the deadliest such episode in decades. Two more episodes followed in June, killing 19 people together. In July, the Bhiwandi garment factory collapsed, killing six people. Other collapses in India have included a hospital in Bhopal in April.

The collapses highlight problems with India’s housing stock and construction standards. Many of the structures that dot Mumbai’s skyline are crumbling and date from the country’s independence in 1947, when they were hurriedly built as part of the city’s emergence as a commercial hub.

Mumbai’s buildings department is known for its corruption, and bribing inspectors and other government officials is considered part of the normal cost of doing business. One result is that many buildings are visibly crumbling. Another problem is rent-control rules that allow tenants to live in apartments for a few dollars a month and even pass those rights on to their descendants, giving landlords little incentive to invest in building maintenance. The city requires extensive approvals for even minor repairs, a process so cumbersome that repairs are often either delayed or done illegally and without consultation from engineers.

India is one of the only countries in the world where buildings as tall as six stories are constructed using a small-batch process of mixing concrete by hand, rather than having trucks deliver premixed concrete. The quality of the concrete can vary considerably with hand-mixing, while premixed concrete is of more uniform quality.

In most of the world, structures more than two stories high require premixed concrete not only because of government rules but also because few other places can find workers willing to carry loads of concrete by hand up more than one or two flights of stairs. In India and Bangladesh, workers routinely carry such loads up five or more flights.

Sheetal Shinde stood at a nearby tea stall with tears in her eyes looking at the rescue operation. “There are five of my relatives in that building,” she said. “They are still trapped inside.”