ATTAPEU TOWN, Laos — The day before this week’s catastrophic dam failure in Laos, the companies building the dam knew that it was deteriorating, and one of them saw a potential trouble sign three days in advance. Yet many people living downstream received no warning of the deadly flood that was about to sweep away villages, farms, livestock and people.

The companies said they had warned Laotian officials of the danger, and some villages were evacuated, but the dam’s collapse killed at least 27 people — many more are still missing — and displaced at least 6,600 others in Laos. On Thursday, state media in Cambodia reported that as many as 25,000 more people in that country were being evacuated from the northern border province of Stung Treng, as the flood surge made its way south.

Now, as rescue workers scramble to find missing villagers and care for others in makeshift shelters, questions are mounting about the speed of the one-party state’s response, the quality of the companies’ work, and whether they could have done more to prevent the accident or alert people to the peril.