5 people were killed and 12 others wounded in the attack in the opposition-held district of Sevre.
Syrian opposition-held district of Sevre in the northwestern province of Idlib was hit by a vacuum bomb attack aerially dropped by Syrian regime on Monday, leaving five people dead and 12 injured.
The wounded including civil defence staff have been taken to local hospitals.
A security source says civil defence personnel were trying to retrieve victims that are trapped in a building which was demolished after the attack.
33 people, mostly women and children suffered from breathing difficulties and vomiting due to chlorine exposure.
The United Nations on Tuesday called for an urgent ceasefire in the divided city of Aleppo, where it said 2 million people lacked access to clean running water, with children at risk of disease.
"The UN is extremely concerned that the consequences will be dire for millions of civilians if the electricity and water networks are not immediately repaired," a statement from Yacoub El Hillo, UN Resident and Humanitarian Coordinator for Syria, and Kevin Kennedy, UN regional humanitarian coordinator for the Syria crisis, said.
Syria has been locked in a vicious civil war since early 2011 when the regime of Bashar al-Assad cracked down on pro-democracy protests which erupted as part of the Arab Spring uprisings, with unexpected ferocity.
Since then, more than a quarter of a million victims have been killed and more than 10 million displaced across the war-battered country, according to the UN.
The Syrian Center for Policy Research, however, puts the death toll from the six-year conflict at more than 470,000 people.