At least three controlled explosions were carried out on suspect devices which had been left in various locations around the city.
The areas around Derry's Courthouse and the Strand Road police station were closed for much of the day as British Army Technical officers attended the alerts.
At a press briefing in Derry this afternoon, the PSNI described how masked men had hijacked vans in two different parts of the city - leaving one outside the courthouse and one outside the police station.
Both decks of the Craigavon Bridge were closed but have since re-opened with nothing untoward being found.
The hoaxes caused severe disruption across Derry, which has been strongly condemned by local politicians and businessmen.
A security alert at a shopping centre in Ballymena has also ended.
In Belfast, motorists have been advised to avoid the city centre area because of a series of security alerts there.
In the Finaghy Road North area of West Belfast - police have erected a security cordon around a bus after two masked men boarded it shortly before three, leaving a suspicious object on board.
A security alert is also continuing on the Malone Road.
Report of suspect device in Newry
Meanwhile, thousands of rubgy fans travelling to tomorrow's Ireland/Scotland Six Nations Championship match will be affected by the security alert which has closed the railway line at Newry.
Three special trains, which had been arranged to transport fans to Dublin for the game, have been cancelled following reports of a suspect device being found on the line.
Translink says that all tickets will be refunded and passengers are being advised to use the additional Translink bus services that have been put on.
