They said the blast occurred during peak late-night shopping after breaking of the fast during the Muslim month of Ramadan.
"It's timing comes with heavy congestion by shoppers," said Yaseen Shalabi who was near the site of the explosion shopping with his family.
There was no immediate claim of responsibility.
The Arab-populated town run by Syrian rebel groups backed by Turkey opposed to Syrian President Bashar al Assad has been relatively quiet since it was hit by a car blast over two years ago.
Main towns in the northwestern border area have in recent years been frequently hit by bombings detonated in crowded civilian areas.
The civil defence forces said that at least thirty were wounded with some seriously injured transferred to local hospitals.
Residents and rebels in the mainly Arab-populated rebel-held northwest have long suspected the Kurdish led YPG who control large swathes of areas in northeast Syria and east of the Euphrates in northern Syria. Others blame groups loyal to Assad.
The bomb exploded in the town of Aziz in Aleppo province. Volunteers with the Syrian Civil Defense, known as the White Helmets, said the blast, just after midnight, killed two children and a woman.
The explosion that tore through the busy market also wounded five civilians and destroyed shops and homes in the area, the paramedic group said. First responders struggled to break through the large panicking crowds in the market, searching for casualties, clearing the wreckage, and putting out fires..
Meanwhile, Britain-based opposition war monitor the Syrian Observatory for Human Rights said at least eight people were killed and 23 wounded.
Türkiye has launched three major cross-border operations in Syria since 2016 and controls some Syrian territory in the north.
