A collision involving two vehicles occurs in the Sydney Harbour Tunnel, causing major disruption for motorists travelling north on Saturday afternoon. Multiple outlets report that the crash brings northbound traffic to a standstill, leading to significant traffic congestion. The incident blocks or slows movement through the tunnel, trapping vehicles in the affected direction and creating delays for commuters and other road users. The reports describe the incident as a traffic-chaos situation as drivers experience severe standstill conditions while responding to the crash and any associated lane closures or slowdowns. The outlets do not provide further details such as injuries, the exact time of the crash, or which vehicles were involved. Authorities are not specifically detailed in the provided summaries. Overall, the coverage focuses on the immediate impact on northbound traffic flow through the tunnel and the resulting congestion in the surrounding transport network.