SHANGHAI, May 22 (Xinhua) -- Shanghai partially resumed its cross-district public transport on Sunday, as part of the city's efforts to restore the public transport system step by step.

       Four main subway lines -- numbers 3, 6, 10 and 16 -- resumed services on Sunday, with trains running from 7 a.m. to 8 p.m. and at 20-minute intervals.

       A total of 273 bus routes also resumed services, covering the city's airports, railway stations and major hospitals.

       Passengers are allowed to use the public transport system only when they have negative result certificates for nucleic acid testing taken within 48 hours. They are required to wear masks throughout their trips.