Residents of a Colombian city were awakened by an alarm that warns them of impending disaster Friday night.

Many in the small town of Mocoa were sleeping and did not have time to evacuate to higher ground, and were swept away by an enormous mudslide after heavy rains caused a nearby river to overflow. The surge of mud killed and injured hundreds and destroyed many homes.

At least 234 died, and 220 were missing in the city of about 350,000. Hospitals struggled to cope with the burden of so many injuries, and some with more serious wounds had to be airlifted to other towns.

Houses in 17 different areas were buried or taken away by the landslide, according to Mocoa’s mayor, José Antonio Castro.