Syrian regime rocket fire killed nine people including three children at makeshift camps for displaced people in the country's last major rebel-held bastion early Sunday, a war monitor said.

The dead included three children among seven civilians, and two unidentified individuals, said the Britain-based Syrian Observatory for Human Rights, which has a broad network of sources on the ground.

An earlier Observatory toll reported six civilians dead, including two youngsters.

It said another 75 people were wounded when more than 30 rockets exploded in several areas, including the camps, west of the city of Idlib in Syria's northwest.

Shelling continued later in the morning at several locations in the area, and rebels targeted government positions in retaliation for the strikes, according to the Observatory.

An AFP correspondent saw flimsy tents destroyed and burned, blood stains and rocket debris at the scene.

At a nearby hospital, the correspondent saw the bodies of two young girls.

Abu Hamid, a camp resident, told AFP: "We awoke this morning and were getting ready for work when we began hearing the sounds of strikes."

"The children were afraid and began screaming", continued the 67-year-old.

"We didn't know where to go. It wasn't one rocket or two, but a dozen. The shrapnel was flying from every direction. We didn't know how to protect ourselves."

The last pocket of armed opposition to President Bashar al-Assad's regime includes large swathes of Idlib province and parts of the neighbouring Aleppo, Hama and Latakia provinces.

Hayat Tahrir al-Sham (HTS), headed by ex-members of Syria's former Al-Qaeda franchise, is the dominant group in the area but other rebel groups are also active.

According to the Observatory, the rocket fire came the day after five Syrian forces members died in shelling by a group affiliated with HTS.

The Idlib region is home to about three million people, around half of them displaced.

They are among the millions displaced internally and abroad by the war in Syria since 2011. Nearly half a million people have been killed.

With Russian and Iranian support, Damascus clawed back much of the ground lost in the early stages of Syria's conflict, which erupted in 2011 when the government brutally repressed pro-democracy protests.

Despite periodic clashes, a ceasefire reached in 2020 by Moscow and Turkey -- which supports anti-Assad rebels -- has largely held in the northwest.