Government forces and their allies have concentrated around Idlib, where aid groups fear that what could be the last major battle of the seven-year Syrian civil war is also the deadliest.
Western powers have warned against a bloodbath, but Damascus and Moscow insist that an offensive is needed to eradicate the jihadists who dominate the province.
In the last few days, sporadic bombings were directed against the armed groups on the margins of Idlib, and on Thursday families began to leave their battered places of origin to seek safety elsewhere.
Stacked trucks with mattresses, metal pipes, plastic tanks and wicker mats could be seen heading to the camps near the northern border of Syria with Turkey.
"We went for the bombings, the crazy indiscriminate bombing," said Abu Naser, who fled in the back of one of those trucks.
"We do not know where to go now, a lot of people fled, what are we supposed to do, sit under bombardment and airplanes?
Another group of hundreds of families fled the southeast of the province in search of other areas controlled by the rebels, said the Syrian Human Rights Observatory.
The head of the observatory, Rami Abdel Rahman, said that "about 180 families, or about 1,000 people" had escaped from those areas since Wednesday night, heading to rebel territory further east.
They fled from Syrian artillery and Russian bombing in villages that are close to government-controlled areas and, therefore, would be more vulnerable to the initial phase of an assault.
Artillery fire also killed one civilian and wounded six others, the war monitor based in Britain added.
& # 39; Retreat from the edge & # 39;
The number of displaced persons so far is small compared to the 800,000 that the United Nations fears could be thrown on the roads, more than a quarter of the population of the rebel zone.
Warning of the risks of an assault on the Idlib regime, French Foreign Minister Jean-Yves Le Drian described the enclave of the rebels as a "time bomb, both in humanitarian and security terms."
Save the Children said more violence would have "devastating consequences" for young Syrians.
"During seven years of war, these children have seen and experienced things that no child should have," said their leader Helle Thorning-Schmidt, and asked the parties in conflict in Idlib to "withdraw from the edge."
The UN, world powers and aid groups hope that a summit on Friday between the presidents of Russia, Iran and Turkey, the three main agents of power in Syria, can avoid an assault.
The trio will meet in Tehran as part of the ongoing Astana process to end the conflict, which has killed 350,000 people and expelled more than 11 million of its homes since it broke out in 2011.
Russia says its priority is to eradicate the jihadist groups from Idlib, and the Foreign Ministry promised on Thursday that it will continue to "kill terrorists" throughout Syria.
"We have killed, we are killing and we are going to kill terrorists … whether in Aleppo, Idlib or other parts of Syria," said spokeswoman Maria Zakharova.
Turkey, meanwhile, already hosts three million Syrian refugees and wants to avoid an attack that would push more towards the border.
Ankara is under pressure from Russia to exert its influence on the rebels in Idlib, but the province is dominated by the most powerful alliance and led by jihadists, Hayat Tahrir al-Sham (HTS).
"We can work together to make those (radical groups) ineffective, the solution is not to bomb or attack all Idlib, without any distinction," Turkish Foreign Minister Mevlut Cavusoglu said on Wednesday.
Blow into the rescue center
Turkish President Recep Tayyip Erdogan said before addressing Iran that an offensive could trigger "a serious massacre," while his US counterpart, Donald Trump, said the outcome of the Tehran summit would be crucial.
"Because the world is watching, that can not be a killing, if it's a killing, the world will be very, very angry, and the United States will be very angry," he said on Wednesday.
Russia has hinted that Idlib's offensive could be carried out in several phases, giving the negotiations the opportunity to continue in parallel.
The next few days could see the launch of a restricted attack on peripheral areas, focusing on the strategic north-south M5 motorway and eliminating the rebels responsible for drone strikes at the Russian Hmeimim air base.
On Thursday, rescue teams said their headquarters in the southern part of Idlib province was forced to close after suffering damage in air strikes.
Mossab al-Qadur, the head of the center in Al-Tamana, told AFP he was inside the building when he was hit by dozens of rockets and missiles.
"When the grenades stopped, we left quickly, and about 15 minutes later, a Sukhoi 24 (Russian plane) aimed at the center, which put him out of commission," Qadur said.