Indian television channels showed flames leaping from the building and thick plumes of black smoke rising into the sky. People trapped on upper floors were seen jumping onto mattresses laid out below.Building fires are common in India due to a lack of firefighting equipment and routine disregard for safety regulations. The cause of this latest fire was not immediately known.It broke out in the morning at Flourish Stay, a bed-and-breakfast in a congested neighbourhood in the south of the city, Delhi Police said in a statement."It is with profound sorrow that 21 persons have been declared dead in this tragic incident," police said.Many of them had come to the city for medical treatment, according to local media reports.India's foreign ministry was in touch with the embassies whose citizens were among those affected by the fire, officials said. The ministry "remains in close touch with the concerned embassies and is extending all necessary assistance," junior foreign minister Kirti Vardhan Singh said on X.Authorities said more than 40 people were taken to hospitals for treatment.Eight were in a critical condition, according to a statement by a nearby hospital.A total of 47 guests were in the hotel when the fire broke out, local lawmaker Satish Upadhyay told reporters.Locals rushed to the site, as firefighters worked to douse the blaze and ambulances arrived to transport the injured.Prime Minister Narendra Modi called the deaths tragic. "My condolences to those who have lost their loved ones," his office said in a statement.'Jumped from the building'Some reports suggested the hotel had just one door for entry and exit and lacked proper ventilation."An inquiry will be conducted, and anyone who has broken norms and is responsible will be immediately arrested," Upadhyay said.Some people trapped on the upper floors of the building jumped onto mattresses laid out by on the street outside, said eyewitnesses. "We got mattresses from a nearby bedding shop because people needed to be rescued," Mohammad Anees, a local resident, told AFP. "Once the mattresses were laid out, five women jumped from the building and landed safely on them."The blaze was eventually brought under control with the help of eight fire engines, police said.The cause of the fire, one of the deadliest blazes in the Indian capital in recent years, was not immediately clear.Electrical short circuits, often caused by poorly maintained wiring, remain the leading cause of fire incidents in India.In March, a fire at a government-run hospital in eastern India killed 10 critically ill patients.The last major fire incident in Delhi killed 43 factory workers sleeping in a building in the city's old quarter in 2019.