LONDON - At least 10 people are believed to have died after a reported blast at a concert venue in the northern English city of Manchester, which police are treating as a possible terrorist incident, the BBC reported on Tuesday. 'Senior national counter-terrorism officers are assembling in London. Early estimates put fatalities at Manchester Arena in double figures,' a BBC reporter said on Twitter. The BBC and Sky News reported shortly before that local police were treating the blast as a possible terrorist incident.