The MTR Corporation said journeys on the Tsuen Wan Line would take longer than usual due to a mechanical defect on Thursday morning.
The railway firm said it is taking three to five minutes longer to travel between Tsuen Wan and Central, although temporary repair work had been completed.
It said engineers found cracks on the train tracks near Tsim Sha Tsui Station at around 8am, and they had added temporary supports to ensure safety.
The MTR said engineering staff would closely monitor the condition and replace that section of track after the trains stop running at night.