Police and other emergency services are seen near the Manchester Arena after reports of an explosion. Police have confirmed they are responding to an incident during an Ariana Grande concert at the venue.

Britain's political parties have agreed to suspend election campaigning until further notice following an explosion in Manchester that killed at least 22 people at a concert by U.S. singer Ariana Grande.

Jeremy Corbyn, the leader of the opposition Labour Party, said in a statement that he had spoken to Prime Minister Theresa May and had agreed that all national campaigning for the June 8 election would be suspended.

May said earlier that the incident in the northern English city was being treated as a terrorist attack and that authorities were working to establish the details of the blast.

"I am horrified by the horrendous events in Manchester last night," Corbyn said. "My thoughts are with families and friends of those who have died and been injured."

Initial signs pointed to a suicide bomber as the cause of the blast, said two U.S. officials who spoke on condition of anonymity.