Police and the air ambulance attended the incident between junction 18 and 19, following a crash at about 17:00 BST on Sunday.
The westbound tunnel was temporarily shut for the air ambulance to take off.
The eastbound stretch was closed as North Wales Police investigated the incident and cleared the scene.
The incident caused long tailbacks as motorists were advised by police to avoid the area and find alternative routes.
The A55 is fully reopen after an accident near the Conwy tunnel closed the eastbound carriageway for almost three hours.