Government forces have been blamed for the attack, which injured at least 75.
The Syrian Observatory for Human Rights, a conflict monitor, said that the shelling followed attacks on Syrian regime forces, which killed five on Saturday.
Those attacks were blamed on Hayat Tahrir Al Sham, a militant coalition that has been linked to Al Qaeda, and is the dominant force in Idlib.
About 3.4 million people live in Idlib, the vast majority of them internally displaced people following the decade-long war which led to as many as 12 million Syrians fleeing their homes amid air strikes by Russia and the government, and the rise of terrorist groups, including ISIS.
Many of the estimated two million internally displaced people live in the province's sprawling tent cities, catered for by international aid organisations. But conditions are grim and malnutrition, disease and a lack of access to clean water are widespread.
Fighting often rages on the edge of the governorate, despite a shaky ceasefire agreement brokered in 2020 between Moscow and Ankara.
With Russian and Iranian support, Damascus clawed back much of the ground its lost in the early stages of Syria's conflict, which erupted in 2011 when the government brutally repressed pro-democracy protests.