Inclement weather and minor hiccups have failed to derail the opening day of a long-awaited $15 billion rail line in Australia’s second-largest city.

Regular services started running through Melbourne’s Metro Tunnel on Sunday, stopping at five new underground stations with platform screen doors and shops.

The maiden public journey left Sunbury in the city’s outer north-west at 9.28am and reached Arden Station at 10.09am before moving on to Parkville, State Library, Town Hall and Anzac stations.

Victorian Premier Jacinta Allan, who has been part of every stage of the project, said she was immensely proud.

She was joined on the first train by Labor MPs, media and her family, with applause erupting as it entered the tunnel.

“It’s absolutely bloody amazing to see this day come,” she said.

The nine-kilometre twin tunnels are the biggest upgrade to Melbourne’s rail system since the City Loop opened four decades ago.

Victorian Premier Jacinta Allan (left) and Transport Infrastructure Minister Gabrielle Williams go for a ride at the opening. Photo: AAP

The tunnel’s five underground stations were bursting with train enthusiasts and curious city-dwellers despite Melbourne’s notoriously temperamental weather sending down buckets of rain.

Staff handed out Metro Tunnel-emblazoned treats such as biscuits, lollipops and mints to commemorate the occasion as performers dazzled commuters.

Firefighters from eight Melbourne stations sought to put a damper on festivities by issuing safety notices.

United Firefighters Union boss Peter Marshall said firefighters did not have the “equipment, knowledge or training to protect members of the public” in the rail tunnel, or a soon-to-open road tunnel.

Allan rubbished his claim, pointing to National Rail Safety Regulator signing off on accreditation for the project.

In the “summer start” period, Metro Tunnel services will run every 20 minutes from 10am to 3pm between Westall and West Footscray on weekdays and every 20 minutes from 10am to 7pm at weekends.

Passengers won’t need a myki card to ride the line on Saturday and Sunday, with travel free across the network at weekends until February 1.

At that point, three lines will be ripped out of the City Loop and the tunnel’s “turn-up-and-go” timetable will begin, with trains arriving every few minutes during peak periods.

Young train nut Mark Steffens was among those who lined up to board the first train after arriving from Perth by plane at 1am on Sunday.

“It’s so good how it’s going to interconnect the lines here and reduce how busy the City Loop is because it’s already over capacity,” the 18-year-old said.

Julius Espinosa, 17, woke at 5am to train into the city from Laverton and out to Sunbury to catch the first service.

“It wasn’t easy but it’s worth it,” he said.

Melbourne’s second underground rail line has been a long time coming.

A Melbourne Metro rail tunnel was part of the then Labor government’s 2008 Victorian Transport Plan. Scope and route changes followed, before the final design was settled in 2016.

Cost escalations pushed the 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 tops $15 billion.

Public Transport Users Association spokesman Daniel Bowen said the tunnel would bring benefits worthy of its huge cost.

“It’s the sort investment you have to make in a city to keep things moving and make sure that people can get around,” he said.

“The City Loop, back in the day, was incredibly expensive as well but I don’t think anyone doubts the benefits that it’s brought to Melbourne.”

-AAP