BUDAPEST: A large explosion “of unknown origin” rocked a building in downtown Budapest late on Saturday, injuring two passing police officers, authorities said. The blast occurred at 10:30 pm local time (2030 GMT) inside or beside a ground floor shop on a major intersection, a police statement said Sunday. Two police officers who were on patrol were injured and taken to hospital, said the statement. The cause of the blast remains unconfirmed, although a news report on public television said security cameras had recorded a bag being left at the scene shortly before the explosion. Unconfirmed police sources also told local media that an investigation had been launched into attempted murder. Initial eyewitness accounts said the large blast sounded like a gas explosion, although Hungary’s rescue agency said no fires were caused. Eyewitnesses also posted pictures on social media of some nails scattered on the road at the scene. A homemade bomb device was likely to have been behind the blast, an explosives expert Attila Ladocsi told M1. According to the channel’s news programme, a person was seen by security cameras placing a bag at the scene shortly before the blast. Police are to give a detailed account of the investigation later Sunday, a government spokesman Bence Tuzson told the MTI news agency. A session of the national security parliamentary committee has been convened for Monday its chairperson told MTI. No information has been released on the injured police officers’ condition, nor confirmation of local media reports that one of the injured was a woman. The explosion, which was heard across large parts of the Hungarian capital, damaged ground floor walls of the building and blew out building and car windows at the scene. “There was a big explosion, lots of smoke, and the window of the hostel I was staying in nearby was smashed,” an American tourist told M1. The surrounding area was cordoned off by police who evacuated buildings at the scene, one of the main thoroughfares of the Hungarian capital. Forensic personnel combed the area for clues through Sunday, while police carried out door-to-door enquiries with residents. The incident comes days before Hungary holds a referendum October 2 on the EU’s quota plan for the mandatory relocation of migrants. The campaign has been marked by fears over public security, and government posters that have strongly linked migration and migrants to terrorism. Prime Minister Viktor Orban, a fierce opponent of the EU’s handling of the migration crisis, called the ballot in order to “send Brussels a message” that it should not force member states against their will.