On Facebook, Manchester Arena confirmed the incident and stated it "occurred outside the venue in public space."
Manchester mayor Andy Burnham tweeted his condolences to families who lost loved ones and praised the city's emergency services, calling this a "terrible night for our great city."
The United Kingdom's national railway police force, The British Transport Police, also issued a statement noting reports of an explosion within the foyer area of the stadium and that no trains or trams are running from the adjacent Manchester Victoria station.
"Officers are at Manchester Arena following reports of an explosion within the foyer area of the stadium at 10.30pm this evening," the statement read. "Emergency services are at the scene and we are working to establish more information regarding the explosion and will provide further updates as soon as possible.
"Please avoid the area whilst emergency services continue to respond to this incident. No trains or trams are running from Manchester Victoria station."
UPDATE: The O2 arena tweeted that Grande's Thursday and Friday shows in London have yet to be canceled but they will advise ticket-holders if that changes.