Commuters face several days of delays after the weekend’s high winds brought down Metro power lines.
Services between Pelaw and South Hylton have been suspended since overhead cables came down near Brockley Whins on Sunday.
Track operator Network Rail say repairs are likely to continue into the second half of this week, and is warning of knock-on disruption for other rail companies sharing the line.
Huw Lewis, head of customer services and communications for passenger transport executive 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 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.”
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.
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.
Storm Desmond caused extensive damage and disruption to the Metro system. 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.
A Gentoo spokeswoman confirmed the property firm had also seen a sharp rise in emergency repair calls over the weekend.