– A crushing military offensive by the Syrian government and its Russian allies in northern Syria has killed dozens of civilians and displaced more than 100,000 people in less than 10 days, humanitarian aid groups and medical officials there say.

The assault in Syria's Idlib Province is part of a push by President Bashar Assad to regain control of strategic highways, and ultimately the country's last major rebel-held area. Clashes, government shelling and Russian airstrikes this month have sparked a panicked exodus that aid workers warn could lead to one of the worst humanitarian catastrophes of Syria's eight-year civil war.

Homes in Maarat al-Numan, the largest city in Idlib's southern countryside and the main target of the escalation, have steadily emptied as a parade of cars streams out, residents say. People are struggling to find medical care and shelter as the number fleeing airstrikes swells.

"People, I swear by God, are sleeping in open air under trees and the temperature at night is near freezing," Shaker al-Humeido, a doctor who worked in Maarat al-Numan, said in a text message. The hospital where he worked had been emptied as fighting approached, and he and his family fled north.

"I am shocked at the size of the tragedy," he said.

Turkish President Recep Tayyip Erdogan warned last week that "massacres" in the province had sent more than 80,000 people fleeing toward Syria's border with Turkey, which already hosts about 4 million Syrian war refugees. But his government, which maintains military outposts in Idlib and enjoys warm relations with Russia, has failed so far to blunt the offensive.

The violence is the latest miserable trial for Idlib, a wellspring of opposition to Assad's government that hosts hundreds of thousands of people displaced by war from other parts of Syria.

The province, with 3 million people, has borne the brunt of a Russian and Syrian air campaign that has struck hospitals and leveled homes and markets, human rights groups say. The province and surrounding areas are largely controlled by Hayat Tahrir al-Sham, an extremist Islamist group that began as al-Qaida's affiliate in Syria and has tried to rebrand itself several times during the war.

Fighting over the last year has taken a disproportionate toll on children, according to UNICEF, which said in a statement on Tuesday that more than 500 children were injured or killed in the first nine months of 2019. At least 65 children have been killed or injured in December alone, the group said.

Dareen Khalifa, a Syria analyst with the International Crisis Group, said Assad's short-term goal has been to encircle and control Maarat al-Numan and the town of Saraqib, about 15 miles northeast. Then, she said, the Syrian army would push west to retake a highway linking Latakia and Aleppo as it attempted to capture Idlib in chunks.

"The problem is, the regime offensive that started in April hasn't been very successful," she said. "So now they are overcompensating by using devastating levels of air force. The casualties and displacement levels are catastrophic.

"If the regime continues and if the rebels don't surrender this will mean the worst humanitarian disaster we've seen in Syria."