The three leaders made an aerial survey by helicopter of Majuli island, Jorhat, Sibsagar, Lakhimpur and Dhemaji districts, which were among the worst-affected in the floods, senior officials said.
They were also expected to survey the Kaziranga National Park, which has been completely submerged by flood waters.
Earlier, Singh and Gandhi reached Jorhat's Rowriah airport from New Delhi by a special flight at around 11:00 AM.
Later in the day, the two leaders would reach Guwahati and discuss the latest situation with ministers and officials.
Singh and Gandhi are scheduled to leave for New Delhi from Guwahati in the afternoon.
The Assam floods have so far claimed 61 lives and another 16 persons have been killed in landslides.
The floods have affected all 27 districts of the state.
