At least 54 people were killed in airstrikes and artillery shelling across northern Syria, part of a long-anticipated offensive against rebel-held areas announced by Russia, a key ally of Syrian President Bashar Assad.
The bombardment hit in besieged neighbourhoods of Aleppo, as well as the surrounding countryside and the nearby rebel-held province of Idlib.
Residents said the aerial campaign intensified yesterday.
Syria's Civil Defence, known as the White Helmets, recorded at least 150 raids, more than double the number of attacks on Aleppo on Tuesday.
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Resident Modar Shekho said warplanes hadn't left the skies over his neighbourhood since 9 AM (local time).
"The helicopters would leave and the jets would arrive," he said by telephone, adding that the helicopters were dropping seven or eight "barrel bombs" at a time "causing a lot of destruction."
"It was frightening," said Hatem, who gave only his first name out of fear for the security of family members living in government-controlled areas. He said he counted more than 20 missiles falling, and a number of nearby buildings were destroyed.
When he and the others emerged, he said they found missiles had landed in the hospital's courtyard, hit the main door and stairs. The hospital's operating rooms, incubators and other equipment were moved underground four months earlier because of repeated aerial bombings of the city.