Torrential rains in central Mexico suddenly flooded a hospital early Tuesday, killing 16 patients, possibly due to the loss of oxygen equipment as the power went out, the national Social Security Institute said.

A video posted on the agency’s social media feed said about 40 other patients survived as waters rose swiftly in downtown Tula, about 60 miles (100 kilometers) north of Mexico City, and flooded the public hospital around 6 a.m.

Video recorded inside the hospital showed knee-deep water as staff frantically tried to move patients.

Later Tuesday, emergency personnel evacuated the hospital, loading patients into ambulances to be taken to other health centers.

IMSS Director Zoé Robledo said the waters knocked out power to the area as well as the hospital’s generators.

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He said the hospital had been caring for 56 patients, about half of them suffering from COVID-19.

Rescue teams of firefighters and soldiers steered boats through Tula’s streets rescuing people from flooded homes.

The town’s central market was completely flooded. In one location beside the river, a jumble of semi-trailers, buses, tanker trucks and cars lodged against each other semi-submerged at odd angles in rushing water.

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Residents carried boxes and bags of salvaged belongings to higher ground.

Tula Mayor Manuel Hernández Badillo said at a news conference, “Today the important thing is saving lives.”