A 50-year-old five-storey building housing a boys' PG collapsed in Satya Niketan near Delhi University's South Campus on Sunday, leaving at least six students dead and many trapped, officials said.
One more body was recovered during late-night rescue operations, taking the death toll to six.
Ten people have been pulled out of the debris so far, of whom four were brought dead to the hospital, and one died during treatment.
Three patients remain admitted and are undergoing treatment, while one underwent limb surgery and another was discharged after observation.
A 19-year-old person was also brought to Safdarjung Hospital at 3.05 pm with minor injuries and was admitted for observation, officials said.
Locals claimed that around 40 people were still trapped under the debris of the building, which comprised a basement and five upper floors.
Delhi Chief Minister Rekha Gupta late on Sunday ordered a magisterial probe into the incident.
"Following an on-site review and based on the preliminary assessment, Chief Minister has ordered a Magisterial Inquiry of the incident and FIR against the building owner," Delhi CMO said in a post on X.
Repair work was underway in the basement of the structure, which was used as a paying guest (PG) accommodation, when it collapsed at around 1.30 pm, a senior officer said.
Locals claimed that collection of water over days of rain in the basement had weakened the building's foundation, leading to it eventual collapse.
Teams of Delhi Police, NDRF, Delhi Fire Service and DDMA, along with fire tenders and CATS ambulances, reached the spot and commenced rescue operations.
Around 200 emergency personnel were involved in the rescue and relief efforts, officials said. Fire and rescue teams worked to clear the heavy debris and search for people who may still be trapped.
The area is marked by narrow, congested bylanes lined with eateries and PG accommodations catering mainly to students.
The densely packed buildings and heavy student presence often leave little room for movement, with locals saying most of the students staying in the locality were from Keralam, Haryana and Uttar Pradesh and study at colleges located across the road.
"The lanes are very congested, and it is difficult for rescue vehicles to reach here faster," a local resident said.
As rescue teams worked through the debris, locals and eyewitnesses also joined the frantic efforts, using their bare hands and whatever tools were available to search for those buried underneath.
A video circulating on social media showed an unconscious youth trapped beneath a slab, with half his face and one hand visible, as locals desperately tried to pull him out.
Delhi Chief Minister Rekha Gupta, Lieutenant Governor Taranjeet Singh Sandhu, Police Commissioner Anurag Kumar, and MP Bansuri Swaraj rushed to the spot after the incident.
Union Home Minister Amit Shah expressed his grief at the deaths.
He said he spoke to the chief minister, the police commissioner, and the NDMA director general for an assessment of the situation on the ground.
The Joint Commissioner of Police, New Delhi Range, DCP Southwest and Additional DCP are supervising the operation, an officer said, adding that the building was known as 'Hostel Daze' and its owner is based in Gurugram.
"The exact number of persons trapped/injured is still not known at present. Further details will be shared as and when confirmed," a statement issued by Delhi Police said.
South Delhi BJP MP Ramvir Singh Bidhuri announced that the government had constituted an inquiry committee to investigate the collapse and initiate strict action against those responsible.
BJP MLA Anil Sharma reached the spot and said people were still trapped inside.
"We are even getting calls from those who are trapped inside. Teams are continuously in touch with those who are trapped inside; we pray to God that all people are safe," he said.
An eyewitness said the incident could have been much worse had it occurred on a working day, as many students from nearby areas had returned home. "Very few were here," he said.
The collapse has also raised questions over the safety of buildings being used as PG accommodations and the enforcement of construction and fire safety norms in densely populated parts of the national capital.
Congress leader and AICC Uttarakhand in-charge Kumari Selja questioned the BJP government over the safety of students living in such accommodations and asked who would be held responsible for their safety.
"What is the BJP government doing? They have forgotten what happened at the coaching centre. A mafia is operating in Delhi. These children are sent away with so many hopes. They are the only support for their parents. Who is responsible for their safety?" Selja said.
Former Delhi Chief Secretary Omesh Saigal said the incident should not be viewed as an isolated case and raised concerns over unauthorised construction in parts of Delhi.
Saigal alleged that some buildings have unapproved blueprints, additional floors added later or substandard construction, and questioned whether authorities responsible for approving building plans had adequately checked their safety.
"Look at the kind of buildings constructed in Delhi, I would say that in some areas, one in five buildings is unauthorised; either the blueprints weren't approved, extra floors were added, or the construction is substandard," he said.
He also called for restrictions on new construction in areas that are already overcrowded and over-built, saying authorities should consider stopping the sanctioning of new building plans in such areas and examine the safety of existing structures.
"At the very least, we should ban new construction in these areas. We must halt new construction, or stop sanctioning building plans, for areas that are already over-congested and over-built. These are the things that need to be addressed," he added.
NSUI president Vinod Jakhar described the situation as extremely grave and alleged that delays in the arrival of medical facilities, police and fire services may have affected the rescue effort.
"Rescue operations are ongoing, and conditions are dire. Almost all the students being pulled out are dead. We tried our best to get those students out; we actually succeeded in rescuing about three of them. Had the medical facilities, medical teams, police, and fire brigade arrived on time, had all necessary resources and responsible officials been present promptly, perhaps more students could have been saved," Jakhar told ANI.
He demanded accountability and justice for the victims and those injured in the incident.
Meanwhile, Delhi Bharatiya Janata Yuva Morcha president Rajat Choudhary said the situation remained serious and appealed for speedy rescue efforts. He said ambulances and doctors were present in large numbers and urged both the Delhi and Central governments to ensure that those trapped were rescued quickly.
Choudhary also appealed to political parties not to politicise the tragedy and instead extend support to the affected families and those involved in the rescue operation.
"This is not the time for politics; those affected were someone's children. Instead of playing politics, one should offer support. The opposition should not do this; they should stand in solidarity," he said.
The locals also raised concerns over the condition and maintenance of other buildings in the area, where several houses have been converted into PGs.
Priyanka, who has lived in the area for over two decades, said, "Buildings here are being constructed up to five-six floors. Many houses have been converted into boys' PGs, with the owners shifting elsewhere. They simply name the properties as PGs, take the rent online and leave the area without even checking back."
She added, "I have not seen any maintenance work ever being carried out. Since it was raining, most of the students were inside rooms, while some had gone home as it was the weekend."
(With inputs from PTI and ANI)