MANCHESTER — A blast on Monday night at a concert in the northern English city of Manchester where U.S. singer Ariana Grande had been performing left an unknown number of people dead and injured, police said.Police said they were responding to reports of an explosion and that there were a number of confirmed casualties and others injured.“We were making our way out and when we were right by the door there was a massive explosion and everybody was screaming,” concert-goer Catherine Macfarlane told Reuters.“It was a huge explosion -- you could feel it in your chest.