ISTANBUL — The mayor of Istanbul is warning that some 90,000 buildings could be at risk of collapsing if a major earthquake strikes Turkey's largest city. The warning comes as the death toll from last week's quake in Turkey and northern Syria now exceeds 40,000.

Istanbul's Mayor Ekrum Imamoglu said on a Turkish TV program that the current estimate of buildings at risk of collapse in a quake is nearly twice as large as the previous administration believed.

This comes after thousands of buildings collapsed following last week's deadly quake and as crews continue working to find victims.

"We have to move very fast" to improve the structures and bring them in line with Turkey's construction codes for building in earthquake-prone areas, Imamoglu said.

He added that some 317,000 structures were granted amnesties.

Turkey sits atop multiple fault lines and is prone to earthquakes.