Metro services between Pelaw and South Hylton are expected to remain suspended for several days following storm damage to power cables.
Network Rail has said repairs are likely to continue into the second half of this week, and this may also cause some delays to other train companies sharing the line, which it owns and manages, after the overhead power cables were damaged near Brockley Whins.
A replacement bus, Route 900 is operating to all stations between Heworth and Sunderland but this is expected to be very busy and passengers should allow extra time for their journey. A second bus, Route 901, is operating between Sunderland and South Hylton.
Metro tickets are also being accepted on local bus services in the affected area.
A spokesman for Nexus said: "We would like to apologise for the inconvenience this will cause Metro passengers, and assure you that both Nexus and its train operator DB Regio are doing all we can to keep people on the move.."
Passengers travelling between Sunderland, Heworth and Newcastle stations only can also use Northern rail trains.
There will be frequent Metro services in all other areas, but these may not run to timetable as trains are turned out of sequence due to the Sunderland line being closed to Metro.
The damage to overhead power cables on the shared line owned and managed by Network Rail at Brockley Whins on Sunday night comes at the end of a weekend in which Storm Desmond caused extensive damage and disruption to Metro lines.
Services between Jarrow and South Shields were suspended late on Friday night until Saturday evening after a large section of factory roof was blown onto the Metro line between Bede and Simonside, bringing down 200 metres of overhead line.
Nexus engineers worked from first light on Saturday throughout the day to remove the obstruction and repair the overhead line.
Elsewhere high winds caused a number of incidents on Saturday including plastic sheeting snagged on the overhead line at Pallion, fallen branches at Ilford Road, and damage to stations at Haymarket, Heworth and Whitley Bay.
Huw Lewis, Head of Customer Services and Communications for Nexus, said: “This has been a very difficult weekend for Metro passengers and, unfortunately, that has continued today.
“I am very sorry for the difficulty this will have caused passengers. We are working closely with our train operator, DB Regio, to provide the best possible service as the day goes on, and to improve the standard of information to Metro passengers.”