Waves of muddy water came flooding out when a dam burst its banks in the Indonesian capital of Jakarta in south-east Asia.
Flash floods up to 4m deep swept towards people's homes as they slept in their beds on Thursday night.
Water poured into buildings in the Tangerang district, and at least 58 people were killed.
The force of the water was so strong telephone poles toppled over and cars were swept along for hundreds of metres.
The thick mud has made it hard for the rescue workers, who have been using rubber rafts to try to reach the survivors.
Soldiers have joined the rescue operation, and are looking for people who may still be trapped in their homes.
People have gathered together, waiting for news of their friends and family.
It's still not known why the dam burst, but officials say the lake behind it became overloaded after heavy rain.