The blaze was started at the property in Rosewood Park, Castlereagh, shortly after midnight yesterday (Saturday). Flammable liquid was poured over the front door of the flat and set alight. A passer-by raised the alarm.
A pregnant woman and her partner in one flat escaped through a window, while two women and two children were rescued from upstairs flats.
“This was a disgraceful incident, which could have easily led to the loss of life of a number of people, including children,” said Mr Long.
“What on earth possesses someone to start such a dangerous fire and put so many lives at risk? I am thankful to the Fire Service for ensuring no-one was killed here.
“It is important those behind this attack are brought to justice. I would urge anyone with any information on it to contact police immediately.”