Thousands of squatters have lived for decades in the areas along the Bagmati River and its tributaries, many of them in fragile wooden and tin sheds.
Early on Saturday, bulldozers began demolishing the buildings. By Friday evening, authorities had reportedly urged residents to evacuate, Bhishnu Prasad Joshi of the police said.
"We are here to help them if they have nowhere to go," he said.
Newly elected Prime Minister Balendra Shah, who is behind the directive, said it was important to remove people from "unorganized and flood-prone" areas.
