An unspecified number of Maoist guerrillas blew up the down line between the two stations, falling in the Chapra parliamentary constituency of Railway minister Lalu Prasad, at around 6.30 am, Railway sources said.
Sources said the naxalites had also planted a bomb on the up track which did not explode.
A bomb disposal squad has been rushed to the scene to defuse the explosive.
Meanwhile, several trains including Muzaffarpur-Delhi Lichchwi Express, Darbhanga-Delhi Sadbhavna Express, New Delhi Guwahati Avadh Assam Express and Gorakhpur-Muzaffarpur inter-city express are stranded at various stations.
Restoration of railway tracks has started, the sources said.