The building, known as Hostel Daze in the Satya Niketan neighbourhood, came down around 13:30 local time (08:00 GMT) on Sunday, with eyewitnesses telling local media that as many as 50 people were inside at the time. At least eight people have been rescued so far, according to reports citing local police.
Construction work had been under way in the basement of the building, which sits a short distance from the Delhi University campus. Many students were in their rooms as there were no lessons on Sunday. A legislative assembly member at the scene said some trapped students had been making calls from under the rubble.
Delhi Police said the building was only 40 or 50 years old. The owner of a nearby shop told news agency ANI that the building was 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," the shop owner said, adding that construction workers were also buried.
An adjacent building was evacuated as a precautionary measure, according to Delhi Chief Minister Rekha Gupta, who said "Every possible effort is being made to safely rescue those trapped."
The National Students' Union of India has 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.