It follows the discovery of a suspicious object on Ballymacarrett Road.
The Sydenham bypass has now been closed in both directions at at Tillysburn due to the ongoing security alert.
Army Technical Officers from nearby Palace Barracks are currently at the scene.
Motorists are advised to seek an alternative route.
Traffic heading to North Down are being diverted off at Dee Street junction.
However, airport traffic is being facilitated say police.
The train line at Titanic Quarter has also been closed.
There are no further details at present.