Brahmaputra River levees had been breached in five places by Thursday, the Hindustan Times reported. Flooding stoked by heavy monsoon rains affected 1,744 villages.
Landslides cut off much of the southern part of the province, officials said. The price of locally grown vegetables rose sharply in Assam because of flooded fields.
"The current flood is the biggest since 1998," Agriculture Minister Nilamoni Sen Deka said. "The river island Majuli is the worst sufferer."
About 200,000 people had taken refuge in government relief centers.
By early Thursday, 22 deaths had been reported, the Hindustan Times said.
Animals have also been affected. In Kaziranga National Park, they have been observed moving to higher ground as the floodwaters rise.