The police booked building owner Hariram and others on charges of culpable homicide, negligence in upkeep of a structure, and endangering safety of others, at the South Campus Police Station
Eyewitnesses told local media that as many as 50 people were inside the five-storey building in the Satya Niketan neighbourhood of south-west Delhi when it came down around 13:30 local time (08:00 GMT) on Sunday.
At least five people were killed and a dozen others are in a critical condition, media reports, citing local police. At least eleven people were said to have been rescued so far, according to reports.
There had been construction work going on in the basement of the building, Hostel Daze, which sits a short distance from the Delhi University campus.
Many of the students staying there were thought to be in their rooms at the time of the collapse as there were no lessons on Sunday.
A legislative assembly member said at the scene that some of the trapped students had been making calls from under the rubble.
Reuters National Disaster Response Force (NDRF) personnel look on at a building collapse in Delhi, while a crushed car is pulled by a digger from the rubble.Reuters
Eyewitnesses told local media that another building beside the hostel had also collapsed. One told news agency ANI that the other building had also been a hostel.
Chief Minister of Delhi Rekha Gupta said an adjacent building had been evacuated "as a precautionary measure". "Every possible effort is being made to safely rescue those trapped," she added. Delhi Police said the building had only been 40 or 50 years old.
The owner of a nearby shop told ANI that it had been under a 100-year lease and that the leaseholder had undertaken excavation work in the basement to expand the hostel and increase their income.
"They strengthened the upper building, but the pillars below were weak," he said, noting that the construction workers had also been buried.
The National Students' Union of India called on the government to investigate the cause of the collapse and hold anyone found responsible to account.
"Negligence with the safety of students and common people will not be tolerated at any cost," it said.Police are searching for the owner of the building, Times of India reports.
Satya Niketan is a densely populated area which houses a large student population, with a number of hostels in the neighbourhood.
Building collapses are relatively common in Delhi, with more than a thousand recorded in the past three years causing dozens of deaths, according to fire department figures.
Poor foundations, inadequate materials and unqualified construction workers were among the common reasons for collapses.
Eleven people, including three children, were reportedly killed last April when a residential building collapsed in north-eastern Delhi.
Before the rescue agencies arrived, students and locals dug through the debris of the collapsed PG in south Delhi's Satya Niketan on Sunday, and formed a human chain to remove the rubble piece by piece in the hope of reaching those buried underneath.
The collapse, which took place at around 1.30 pm, turned a narrow lane near Delhi University's South Campus into a site of frantic rescue operation. Students rushed to where the building stood only minutes ago, many looking for friends and juniors who lived in the five-storey building, while locals began pulling away whatever they could with their bare hands
"We heard a very loud rumbling sound and suddenly the chairs we were sitting on started shaking. It felt like an earthquake. Then we saw a huge cloud of dust moving towards the right," said Abhishek Mishra, a first-year student at Delhi University's Law Faculty, who was near the building.
"Everyone started running towards the building. There were a lot of students and locals at the spot. We all pitched in and started removing the debris," he said.
Students and residents began passing the smaller pieces of debris from one person to another, as they tried to create space for people to enter the wreckage. "We formed a human chain because there was so much rubble and it had to be cleared quickly," he added.
They removed plates, plastic bottles, broken pipes, toilet parts, chunks of concrete and twisted iron rods by hand.
JCB machines were brought in to clear the heavier rubble, but students continued to help, picking through parts of the rubble that could not be shifted mechanically.
"I knew many of the students who were staying there. That is why when the building collapsed, students from around the area immediately came out. Nobody was standing there waiting to be told what to do. People just started helping," he said.
The collapsed PG was adjacent to a temple, next to which stood an MCD office. Students at the spot claimed that the gates of the civic office were initially shut, and they pushed them open to create additional space where the rubble and construction-and-demolition waste being cleared from the site could be kept.
Several students said the collapse exposed concerns related to the safety of PG accommodations in the area.
Students said the building was extremely old but was repainted every year before the start of the academic session, giving parents and others the impression that it was relatively new and well maintained. They also alleged that inspections of the building were rarely carried out.
"Between July 15 and August 20, a lot of students come here because of college admissions. These PGs are made to look attractive -- they have balconies, good decor and spacious rooms. Parents also see that and assume the place is safe," a first-year student said.
"But nobody checks the fire NOC. Nobody checks the construction. The building was already tilted quite a bit. It was a standalone structure and did not have proper support from three sides," another student alleged.
Construction work was under way in the basement before the collapse, a senior police officer said. Locals alleged that water had accumulated there after days of rain and that a wall was being removed as part of the work. These allegations could not be independently verified.
Students also alleged that the response at the site became a source of frustration for many who were trying to help.
"When the authorities came, they were scolding us for being near the site. But we were there because the rescue work was moving slowly and we were trying to help. If people are trapped and the work is slow, students will naturally try to do whatever they can," said Abhinav, a third-year BSc student.
Students and locals later alleged that the NDRF arrived late and that there was a lack of coordination between the agencies involved during the initial response. The allegations could not be independently verified.
Two NDRF teams comprising 70 personnel and a canine squad were eventually deployed at the site. Oxygen cylinders were also dropped beneath the debris for people who might still be alive.
The narrow lanes, packed with PGs, eateries and shops, made movement of rescue equipment difficult.
A girls' PG adjacent to the collapsed building was evacuated as a precaution. The girls were taken to ARSD College, where they were provided food and other assistance, locals said.
Mishra said the problems facing students in the locality went beyond the structural safety of individual buildings.
"Students come here because this is close to their colleges, but they have to compromise on basic amenities. Waterlogging is common during the monsoon and the quality of food in many PGs is also very poor," he alleged.
"When students first arrive, the food is good. After two or three days, the quality deteriorates. Sometimes there is barely any dal, only water. Students have even found insects in their food," he claimed.
By evening, rescue personnel had taken over most of the operation, with heavy machinery clearing the larger sections of the collapsed structure.
Most of the students staying in the locality are from Keralam, Haryana and Uttar Pradesh and study at colleges across the road.
Some students who had come to Satya Niketan looking for PG accommodation said they were shaken by the collapse and would now avoid taking a PG in the area. They said colleges should expand their hostel infrastructure to accommodate more students, so that those coming from outside Delhi do not have to depend on privately run PGs for accommodation.