It is understood the incident was not a car bomb attack, with officers believing a small-scale device was used.
A Police Service of Northern Ireland spokesman has said:
A number of businesses and streets in the Cathedral area of Belfast have been cordoned off following a small explosion.
It occurred at about 6.45pm as police were checking reports of a suspicious object.
At this stage there are no reports of any injuries.
More top news
Mild, muggy air gives way tomorrow
McDonald's has now extended its breakfast menus to all day - but only in the US.
Theresa May and Boris Johnson gave markedly different speeches at the Conservative party conference, Chris Ship reports.