BANGKOK — Prime Minister Yingluck Shinawatra said Friday that she would take direct command of flood control in Thailand as Bangkok took the risky step of opening its floodgates and as criticism of the government mounted after days of disorganization and conflicting messages.

Until now, local authorities throughout the country have been making some of their own decisions about how best to deal with the floods, the worst in decades, adding to the confusion created by government ministers’ issuing contradictory directives. But Ms. Yingluck said Friday that she would begin strictly enforcing a natural disaster law that stops short of a state of emergency but that gives her the right to make final decisions on emergency steps. It also includes punishments for those who do not follow her instructions.

Ms. Yingluck, in office just two months, said the formal structure of the law, The Disaster Prevention and Mitigation Act, was needed because some officials had disobeyed her instructions, hampering overall flood control.

“For example, I ordered the opening of water gates and was told that all were open, but when we checked on the ground, it was a different story altogether,” she said. “So we will need to issue a written order to be sure everything is clear.”