Police are warning of a 'large bump' under the surface of the Mountain Road which has appeared overnight.
The constabulary says it's developed on the Hillbery section of the highway on the Ramsey-bound carriageway.
Officers says the Department of Infrastructure has been notified and is assessing the cause.
They add, as a result, the area may be subject to to works in the following hours which may disrupt travel in the area.
Mountain Road partly reopens
Island resident claims £125,000 National Lottery prize!
Man who bit off ear in public TT attack has appeal thrown out
Northern Civic Amenity Site reopens from Monday
Smudge the Cat sparks rescue after being locked in shop!
MHK hits out over UK's assisted dying announcement
DJ and former Island resident dies after battling cancer
Nursing organisation to contact staff over pay offer