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
A man who used a pickaxe and sledgehammer to ruin Donald Trump's Hollywood Walk of Fame star has avoided jail.
Wet, windy and turning wintry
A bull which escaped from an abattoir led police on a two hour wild goose chase through the streets of New York.