Disruption has been reported to services between Bidston and Wrexham Central.
It is understood a digger on the back of a low loader wagon struck the bridge at Cefn-Y-Bedd.
All lines are currently reported as being blocked.
A Network Rail spokeswoman said:
“Lines are currently blocked due to the bridge strike. A vehicle struck the bridge at roughly 11:40, the vehicle is not trapped, and no damage can be seen.
However, as it is classed as a red bridge, it must be assessed by a structural engineer before we can re-open.
Our Mobile Operations Manager is currently traveling to the site to asses the bridge.”
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