The rhino, which strayed to Rani Chapori in Sualkuchi from Pobitora Wildlife Sanctuary on Sunday, was not spotted but the district administration claimed it was somewhere in the vicinity and could have taken shelter in the mud after eating.
Forest guards searched the area for the rhino without results.
An IAF helicopter, requisitioned by the state government to airlift it to safety, did not operate today.
The rhino was eating and responding well till yesterday, officials said.
A round-the-clock vigil was being maintained by forest guards, river police, district administration employees, local people and veterinarians.
Food, mostly fodder and bananas besides medicines, was being supplied regularly and the rhino was eating well, they said.
The forest department had planned to tranquilise and translocate the rhino to a safer habitat within the next few days but was hesitating as the water level of the Brahmaputra was high and the animal might run to the river soon after tranquilising which might prove to be fatal.