Turkey and Russia's leaders agreed to the ceasefire deal on Thursday, after talks in Moscow to contain a conflict that has displaced nearly a million people in three months.

Residents and fighters in the region said main front lines that have seen heavy air strikes by Russian and Syrian jets, and intense Turkish artillery and drone strikes on Syrian President Bashar al Assad's forces, were quiet hours after the ceasefire came into effect at midnight.

Witnesses said there was only sporadic fire from machine guns, mortars and artillery by Assad's forces and Iranian militias on some front lines in northwestern Aleppo province and southern Idlib province.

In other areas, scattered fighting began to subside, activists said.

"In the first hours we are witnessing a very tense calm from all warring parties," Ibrahim Al-Idlibi, an opposition figure in touch with rebel groups on the ground said.

"Everyone is aware that violations by any side would be met with a response. But this a very fragile truce."

Syrian state media did not report the latest ceasefire deal and the opposition cast doubt it would last amid criticism that it does not address a main Turkish demand that Syrian forces withdraw to the edge of an Idlib buffer zone agreed in Sochi between Russia and Turkey in 2018.

This time, they agreed to establish a secure corridor near the M4 highway, which runs east to west through Idlib, and hold joint patrols along the road from March 15.

Wresting control of the highways in the northwest, two of Syria's most important pre-war arteries from insurgents has long been a main goal of the Russian-backed campaign in a bid to shore up Syria's sanction-hit economy.

To the dismay of Assad's opponents, the agreement did not mention a safe zone where millions of displaced people could shelter and from where they could return to the homes they fled to escape the Russian-backed offensive.

"No one has mentioned a safe zone or areas of withdrawal. There is no pullout and where will the displaced go?... they would never accept going to regime areas. What we have heard today is not comforting," said Ahmad Rahhal, a former general in Syrian government forces who defected to the opposition.

The United Nations says the offensive has uprooted nearly a million people, the largest exodus of the nine-year war.

"These are modest results compared to the massive buildup in Turkish troops along the border and inside Syria," Rahhal said referring to more than 15,000 troops that Syrian opposition sources say Ankara had brought in to halt advances deep into Idlib province by the Russian-backed offensive.

There have been several ceasefires over Idlib. They collapsed after the Russian-backed forces pressed their offensive and gained ground.

Australian Associated Press