NSB officials couldn't operate any of their trains after technical trouble caused signal failure that hit remote controlled operations of the lines.
That meant traffic controllers could no longer see on their screens where the trains were on the tracks, and service was curtailed for safety reasons, to avoid collisions.
The problem, which cropped up around 7am, was believed to be in a cable, and repair workers were scrambling to correct it.
Regional trains from Halden, near the southern Swedish border, had to stop at Ås station, while local trains were held at Ski.
Short summer staffing made it difficult for NSB to replace the trains with bus service for commuters. NSB officials couldn't immediately say when service would resume.
