At least 500 civilians have been killed in the Russian shelling of Kharkiv, Ukraine’s second largest city, since the start of the war, the city’s emergency services agency said on Wednesday.

The true number of deaths could be much higher, the agency said in a statement on Facebook, noting that emergency workers were continuing to scour the rubble of residential neighbourhoods for more bodies, often under fire.

Having failed on several attempts to take the city, Russian forces have unleashed a vicious campaign of shelling against civilian targets, reducing Kharkiv — a once vibrant city of nearly 1.5 million people — to ruins. Just in the past day, shells hit several apartment buildings and a school, the agency said. At least 189 people have been rescued from damaged buildings since the start of the war.

“My dear heroes, today is another day of war,” the city’s mayor, Igor Terekhov, said in a video address to Kharkiv residents on Tuesday evening. “I understand how difficult this is, but we need to hang on.”

More than 600 buildings have been destroyed in Kharkiv, mayor Ihor Terekhov said. “Schools, nurseries, hospitals, clinics have been destroyed. The Russian army is constantly shelling (us) from the ground and the air,” he said.