Despite the efforts of paramedics at the scene, a man and a woman riding a motorcycle died.
"It looks like the motorcycle has at some stage crashed into the median barrier - the big concrete median strip," police Inspector Marty Parker said.
"Our sympathies go out to the families of the deceased."
It appeared the motorcycle, travelling north out of the city, was the only vehicle involved in the crash, which happened shortly before 1pm today.
Mr Parker said serious crash investigators were continuing to piece together what happened.
No further details about the dead riders were immediately available.
The crash closed traffic through The Terrace tunnel on State Highway One - the main route in and out of central Wellington - for about three and a-half hours until 4.30pm.
This caused gridlock on central city roads as cars were often moved at less than walking pace along the main city bypass and busy connecting roads, such as Taranaki St and The Terrace.
Ambulance spokesman Dan White said paramedics treated the man and the woman at the scene, attended by two ambulances and an ambulance 4WD. Two other ambulance 4WDs were stood down before reaching the crash site.
