Melbourne motorists could face road closures and delays for the rest of the day with CityLink still unable to tell drivers when a computer glitch that shut down two main road tunnels will be resolved.
The tollway operator of the two tunnels is yet to find the cause of the glitch that ground morning peak hour traffic to a standstill from 5am (AEST) on Wednesday.
"I don't have a time frame at the moment," a CityLink spokesman told AAP.
Melbourne's Burnley and Domain tunnels were closed after CityLink's neon speed and lane-changing signs suddenly stopped working.
CityLink infrastructure manager Warren Gourley said he could not guarantee the tunnels would be opened in time for evening peak hour.
"I would certainly hope so. At this stage it's still (too) early to call," he told Fairfax radio on Wednesday.
"Our team is very much focused on finding the root cause and getting our system back online."
The tunnels connect Southbank, Melbourne's CBD and Richmond under the Yarra River, with the closure causing gridlock on Melbourne's inner-city roads.
Traffic is heavy inbound on the Monash and West Gate freeways and all roads around the CBD.
The tunnel closures even backed up traffic on other roads, which then delayed some tram routes by up to an hour.
"The worst-affected routes are those which cross Punt Road and Hoddle Street," Yarra Trams said in a statement.
Racing at Wednesday's Ballarat meeting has also been delayed due to the closure of the tunnels.
"The decision was made in mind of the potential impact the traffic issues could have on participants' ability to arrive in Ballarat on time," the Racing Victoria website reported.
CityLink says it closed the tunnels because the IT problem affected incident detection and safety systems that are activated in the case of an accident.
The network problem also affected the back-up system.
It remains unknown, however, if motorists will be able to get a refund because of the CityLink delays.
"Our policy is that people who were caught up in the initial closure of the tunnel, they should call the call centre," Mr Gourley said.
"We rely on getting the message out to people so they're informed on the potential of delays."
Drivers of heavy vehicles travelling from Melbourne's east are advised to exit the Monash Freeway at Warrigal Road.
Motorists travelling from the west are advised to use Kings Way.