A long line of vehicles was seen on Friday leaving the opposition-held city of Maarat al Numan which has borne the brunt of the attacks, which included air strikes, they said.
"The exodus is in the thousands. It's a humanitarian catastrophe, we are seeing people walking in the streets and people waiting near the homes for cars to take them out," said Osama Ibrahim, a rescue worker from Maarat al Numan.
Air strikes killed six people overnight in Maarat al Numan and 11 were killed in villages in the area, rescue teams said.
Hundreds of people have been killed this year in attacks on residential areas in the region, according to U.N. agencies, though a Syrian and Russian military campaign launched at the end of April had subsided in August under a fragile ceasefire.
Syrian state media said the Syrian army had pushed into several villages southeast of Idlib.
Rebel fighters, who say the Russian and Syrian forces are implementing a scorched earth policy as they advance, said villages seized included Um Jalal in southern Idlib province and Rabea and Harbiya in eastern Idlib.
Russia and the Syrian army, which is loyal to President Bashar al-Assad, deny allegations of indiscriminate bombing of civilian areas and say they are fighting al Qaeda-inspired Islamist militants.
Turkish President Tayyip Erdogan, who reached an accord last September with Russia to contain the fighting and whose country is seen by many civilians in opposition areas as a protector, has warned of a renewed refugee influx.Erdogan said on Thursday 50,000 people were fleeing Syria's northwestern region of Idlib. He did not say whether any of the people fleeing had entered Turkey.