Images of death and destruction from the northern province of Idlib in Syria have flooded social media, with local activists and aid workers saying shelling by Russian and Syrian government warplanes in the area has intensified.

Rescue workers from the Syrian Civil Defence (SCD), a volunteer search and rescue team, say that at least 18 civilians have been killed and more than 45 wounded in the continuous bombardment and a gas attack on the rebel-held province since Sunday night.

"The Russians are in a frenzy. They're going mad. The shelling is ongoing throughout the day and night. The warplanes are hitting residential areas," Hadi Abdullah, a local journalist, told Al Jazeera by phone from the town of Kafr Nabl in the northwestern Syrian province bordering Turkey.

"The massacres started yesterday night. The whole area was vibrating. About 12 homes came crumbling down," continued Hadi, describing the attacks on the town on Sunday night.

The uptick in attacks comes after fighters from the Hay'et Tahrir al-Sham group shot down a Russian warplane and killed its pilot on Saturday.

While Russia - the Syrian government's main ally - says it is targeting rebel fighters, locals say the majority of the attacks have been on residential neighbourhoods and hospitals.

The shelling spanned several areas, including Massaran, Khan al-Sabil, and Idlib city, where aid workers say many remain trapped under the rubble.

The main hospital in Maaret al-Numan, east of Kafr Nabl, has stopped working after it was hit by air raids, according to the SCD - also known as the White Helmets.

"About 10 air raids hit the hospital. It was a disaster," said Hadi, who had rushed to the scene.

"The most difficult and heartbreaking scene was when the volunteers were quickly pulling the babies out of the hospital. I can't get the image out of my head," he recalled with a trembling voice.

At about 1am, Hadi headed to film events in Idlib city, where they had heard a Russian warplane targeted a residential building.

"A whole seven-story building came crashing down. The level of destruction is unreal," said Hadi.

Chlorine gas attack

Volunteers with the SCD also reported a suspected chlorine gas attack on the town of Saraqeb on Sunday night, which wounded nine, including three aid workers. This is the second gas attack in two weeks.

"At about 9:20 pm local time (7PM GMT), two warplanes dropped two barrels containing chlorine on a heavily populated civilian area in Saraqeb," Laith Abdullah, an aid worker, told Al Jazeera from Saraqeb.

"There was gas and smoke everywhere. Everyone was suffocating - people were screaming out 'ambulance'," Laith continued.

"It is difficult to describe; it is difficult to explain the amount of pain we were in and how much we were suffering."

'Doomsday'

Idlib province is one of the few remaining areas in Syria where fighters opposed to President Bashar al-Assad's government are putting up a fight.

While Idlib city is dominated by Hay'et Tahrir al-Sham (HTS) - a former al-Qaeda affiliate - some 40 other armed groups loyal to the Free Syrian Army (FSA) also operate in other areas of the province.

The FSA is a loose conglomeration of armed brigades made up of Syrian army defectors and civilians, which receive financial and logistical support from the United States, Turkey, and several Gulf countries.

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Idlib was included in a Russian-Iranian-Turkish deal for de-escalation zones aimed at halting fighting and offering safety to civilians, but it has continuously been targeted.

The province is strategically important for the Syrian government and Russia due to its proximity to the coastal region where the Russian-operated Syrian Khmeimim airbase sits.

Reporting from the Turkish-Syrian border, activist Ibrahim Ismail estimated there were "more than 150 raids in just half an hour" on Sunday night.

"Yesterday night was horrible. People are describing it as Doomsday and saying there were more than eight warplanes in the air. The shelling is heavy and arbitrary," Ismail told Al Jazeera.

Follow Zena Tahhan on Twitter: @zenatahhan