Three columns of Army on 14 August were deployed in flood-hit Katihar district for the relief and rescue operation.
The central help came after Bihar Chief Minister Nitish Kumar on 13 August sought help of the Army and Air Force as the flood situation worsened in the state.
Overflowing rivers from Nepal have played a major spoilsport in four northeastern districts - Kishanganj, Araria, Purnia and Katihar.
Supaul, Saharsa, Bagha, Gopalganj, Madhubani, Sitamarhi, Khagaria, Darbhanga and Madhepura districts are the other districts which have been affected by floods.
Lakhs of people have been affected in these districts.
Pratyay Amrit, Principal Secretary, Bihar Disaster Management, told ANI that "we are sending three columns of Army to Kaithar".
He further added that "a National Disaster Response Force (NDRF) team will also reach there and a State Disaster Response Force (SDRF) team is already there".
River Bagmati in Sitamarhi and Gandak in Gopalganj continue to flow above the danger mark.
Ten NDRF teams have already been deployed in the state and six more teams joined on Monday.
"One team is heading toward Gopalganj, we are sending three teams to Sitamandi and one team to Motihari," Amrit said.
He said that the NDRF teams are being used for the purpose of evacuation.
The Disaster Management Department has asked people living in low-lying areas to move to higher grounds.