The Birkenhead Tunnel was closed in both directions on Friday evening after a two-car crash.
The incident caused major disruption to rush-hour traffic.
Emergency services were called to the scene at around 6.15pm, with fire, police and ambulance in attendance.
Two men were outside their vehicles before fire crews attended, a fire service spokesman said.
It is unclear if anyone was injured.
The tunnel was reopened at around 7.45pm.