The deceased in the blast included 12 children, the monitor said.

"The death toll is expected to rise because there are some people in critical situation, and because there are still missing people," read the Syrian Observatory for Human Rights website.

Speaking further on the matter, the UK-based monitor said: "The Syrian Observatory for Human Rights published this morning that information indicated that it was caused by the explosion of an ammunition depot of an arms dealer who works with Hayyaat Tahrir al-Sham, the explosion took place at the bottom of a residential building in Bab al-Hawa Square area inside the town, which caused the collapse of the building over its residents, the majority of whom are of displaced people from Homs province."

Idlib is currently the last major rebel-held area in the terror-hit nation.

Representative Image of Syria: UN website