COLOMBO, Sri Lanka — The government of Sri Lanka assessed the damage on Sunday from widespread flooding and devastating mudslides, as the death toll from the twin disasters rose and nearly half a million people were displaced from their homes.

The state-run Disaster Management Center on Sunday announced that 151 people had been killed and 112 others were missing. It said the flooding was the worst since torrential rains soaked the island nation in 2003. The authorities estimate that more than 1,800 homes have been damaged and 442,000 people affected.

Some towns were under 18 feet of water, and the navy sent boats and armored vehicles to search for survivors. They moved about 2,000 residents to safer locations over the weekend.

The authorities have ordered residents to evacuate the banks of three major rivers — the Nilwala in the south, the Gin in the west and the Kelani, which runs through the capital, Colombo — fearing that they will overflow. Even though water levels were receding by Sunday night, disaster management officials were wary as more rain was expected in the southwestern parts of the island in the next few days.