Hanoi Railway Transport Jsc, the northern operator, reduced trains between Hanoi and northern port city Hai Phong to a single daily pair from Monday instead of the usual two.
Earlier, it had also suspended trains connecting Hanoi with northern localities like Lao Cai Province, home to famous tourist town Sa Pa, and Yen Bai Province.
Railway operators have also refused passengers at stations in Hai Duong Province, Vietnam's biggest Covid-19 hotspot.
Vietnam has been struggling with a new Covid-19 outbreak since Jan. 28 after 55 clean days. It has recorded 803 community transmissions, with authorities ordering suspension of major spring festivals amid rising fears.
Vietnamese, especially Buddhists, have a long tradition of visiting pagodas and temples in the first lunar month to pray for peace and luck in the new year. It is estimated over 70 percent of the local population are either Buddhists or follow Buddhist practices.
The country has over 3,000 kilometers of railtrack, none of them high speed.