Incessant heavy rains in Arunachal Pradesh and the affected districts triggered the first wave of floods with 75,000 people being displaced as their dwellings were washed away, the officials said.
The state government, after sounding the alert, directed the National Disaster Management teams and district administrations to provide rescue, medical and relief materials to the affected people, they said.
The road link between Assam and Arunachal Pradesh through Dhemaji district has been severed following the flood waters running over National Highway-52 at Samarajan.
The rising waters of the Brahmaputra were also swelling the streams inside the one-horned rhino habitat Kaziranga National Park in Golaghat district, Park sources said.
A report from worst-hit Lakhimpur district said more than 150 villages with around 1.2 lakh people were submerged by the Brahmaputra and its tributaries flowing above the danger mark.
The North Lakhimpur College area of district headquarters Lakhimpur town was waterlogged by the Sondi river, while the Ronganadi river overran 60 villages under Lakhimpur revenue circle (RC).
Rain-fed river Subansiri entering the state from Arunachal washed away the homes of 120 families following erosion at Borsapori, Nahori and Kolakhuwa areas, the officials said.
The Kakoi river affected 20 villages under Kodom RC and Boginadi river hit 10 villages under Boginadi RC. A part of NH-52 was breached at Baghinijan near Podumoni temple last night but was repaired today by the Border Road Organisation to enable movement of small vehicles.
In neighbouring Dhemaji district, 115 villages with over one lakh population have been affected by the ravaging floods and around 40 villages have been submerged by Simen river under Jonia sub-division.
River Jiadhol broke a dyke affecting 60 villages under Machkhowa RC, river Singara overran 15 villages under Naoboicha RC and river Ranganadi 10 villages, they said.
Another 15 villages under Narayanpur RC have been affected by the deluge, besides 25 villages submerged due to breach of an agricultural dyke at Duprang.
Kaziranga National Park's four ranges of Burapahar, Bagori, Arimora and Kohora have been submerged following erosion on its north-west side and the waters rushing in to swell up the streams inside which are now overflowing.
Stating that the animals inside were safe as they had taken shelter on the highlands, the Park sources said 75 forest security camps had been alerted, 125 country boats pressed into service for patrolling and Section 144 CrPC promulgated on the NH-37 passing by the Park for the animals' security.