The attack happened on the Antrim Road area around 4.30 pm.
The PSNI say officers received a report that a derelict building was on fire at the corner of Salisbury Avenue.
Detective Inspector Mary White, of Musgrave Reactive and Organised Crime said: “We are treating this incident as arson with intent to endanger life.
“Adjoining premises had to be evacuated and there was significant traffic disruption for several hours as firefighters dealt with the blaze.
“I would appeal anyone who witnessed any suspicious activity in the area prior to the fire starting, or anyone who has information that could assist in our enquiries to contact police.
“We are particularly keen to hear from anyone who saw a male aged in his forties wearing a denim jacket and light trousers in the vicinity to get in touch.
“I would appeal directly to this male to get in touch with us to assist in our enquiries. The number to call is 101 quoting reference 870 of 4th July.
“Alternatively, information can be given anonymously through Crimestoppers on 0800 555 111.”