A $15 billion train line's switch to full services has been derailed by a fault that left commuters trapped in hot carriages for hours.
Services on Melbourne's Metro Tunnel were thrown into chaos from a "sagging" overhead cable near Hawksburn Station about 5pm on Tuesday.
Passengers on two trains closest to the fault were stranded for up to two hours before being allowed to disembark and walk to nearby Malvern Station.
The power fault caused knock-on cancellations on the Cranbourne, Pakenham and Sunbury rail corridor for the remainder of the evening.
Metro Trains reported services were running well on Wednesday morning after the issue was fixed.
Premier Jacinta Allan apologised to commuters for the widespread disruptions, which came on the second day of ramped up weekday services since the "Big Switch".
"It caused a lot of disruption for many passengers who were trying to get home at the end of a work or school day," she told reporters at state parliament on Wednesday.
It was likely up to 2000 people were stranded with limited water or support, Public Transport Minister Gabrielle Williams said.
"It's a considerable period of time," she said.
"I can completely understand why those affected may have been quite distressed."
The delay in offloading passengers was due to safety concerns for Metro Trains staff and the cause of the sagging cable remains under investigation.
"Early indications are it's not related to the Metro Tunnel or the timetable at all," Ms Williams said.
Passengers on the two trains can apply for government-funded compensation in the form of a day's free travel, equating to $11.40.
Opposition public transport spokesman Matthew Guy said the incident was a disgrace and suggested it would happen again.
"It was third-world conditions: 1200 people trapped on high-capacity trains in the middle of stations and they've got one small ladder to get them off," he said.
"No air conditioning, 30-something degrees in Melbourne, trapped on a train for two-and-a-half hours.
"This is the government's Big Switch. Well it's a big failure."
Metro Tunnel opened with a soft launch in late November before moving to full services on Sunday.
The 9km twin tunnels and their five underground stations are the biggest upgrade to Melbourne's rail system since the City Loop opened four decades ago.
Several cost escalations pushed the tunnel's price tag for taxpayers to $13.48 billion, up from an original estimate of $10.9 billion.
After factoring in extra payments from builders, the total project cost was estimated to top $15 billion.
