Three LPG cylinders exploded one after another inside a house in Chandigarh's Burail area on Monday evening, injuring at least four people, police said.Locals alleged that LPG was being illegally refilled into smaller cylinders. (ANI)The impact of the back-to-back blasts damaged the house where the explosion occurred and left cracks in the walls of several nearby homes, police said.Residents rushed out of their houses after hearing the loud explosions.Police teams and fire tenders reached the spot soon after receiving information about the blast. The injured were shifted to a hospital, a police official said.Also Read | PCMC eyes ‘LPG-free city’ tag, pushes housing societies to adopt piped natural gasAuthorities are yet to ascertain what caused the explosions.However, locals alleged that LPG was being illegally refilled into smaller cylinders at the house where the blast took place.The police said at least 10 cylinders were recovered from the site.Asked about allegations of black marketing of LPG cylinders in the area, a police official said, "These things will be checked and is part of investigation. When we reached, our priority was to rush the injured to hospital."Several residents claimed illegal refilling of cylinders is common across Burail. Many alleged that LPG cylinders are routinely filled and sold illegally in residential lanes, posing a serious risk to public safety.Black marketing of cylinders is being done while administration is sleeping, a local woman alleged. There is so much encroachment in Burail's lanes that even vehicles cannot move freely, she alleged."Such incidents put lives of Burail residents at risk," she said.Another resident said that people living in nearby houses rushed out after hearing loud sounds.He said 10-12 cylinders were kept "illegally" where the incident took place.