A lane of the Westlink countrybound in now reopened following a crash thought to have involved a lorry.
Police say the incident took place near Roden Street.
Two lanes remained open to drivers making their way towards the M1, but motorists were being advised to expect delays.
Trafficwatch NI tweeted: " A12 Westlink RTC continues heading towards M1 J1 - outer lane 3 currently obstructed after Mulhouse footbridge - car facing wrong direction @PoliceServiceNI directing traffic - passable but long knock on delays ."
