(CNN) — "Ri-i-ide the night train with me..." the words echo along the corridor, bouncing off the white tiles and drifting up the escalator at London's Oxford Circus underground station.
Singer Charlotte Campbell dances on the spot around a microphone stand decorated with fairy lights, as a passer-by throws a handful of coins into her guitar case. It looks like being a long and profitable night.
Campbell, 26, grew up on the far reaches of the Central Line, in the northwestern outskirts of London. Now she spends several days a week busking below ground.
She's one of thousands of people enjoying the festive atmosphere on a historic night for London -- after more than 150 years the Tube will run 24 hours a day on Friday and Saturdays.
CNN took to the trains on Friday, riding around the capital, talking to people traveling and working below the streets on the night when London truly became a 24-hour city.
Buzz of excitement
It's 11.20pm, the bars and restaurants of the West End are still packed, people are spilling out onto the streets, weaving their way around neatly-stacked pyramids of trash from the stores nearby.
Tourists dance as a percussionist bashes out a tune on plastic pots and metal pans, and a queue forms at a noodle bar.
24-hour tube arrives on the London Underground. Tube enthusiast Geoff Marshall talks us through the history of the capital's underground network.
At Oxford Circus, the city's busy shopping street, tattered copies of the Evening Standard newspaper litter the steps as people stream down into the station.
"London is a 24/7 city, and it needs a transport system that enables that — not just for the social scene, but for people working in London," Griffiths says.
He expects 100,000 additional passengers every Friday and Saturday night, and thinks the numbers could go higher.
Whoops of joy
London's mayor, Sadiq Khan, was among the first passengers on the city's Night Tube.
"It's a relief to be up and running," says station worker Latoya, who has been doing night shifts since April to prepare.
As incomers whoop with joy to discover that the trains really are still running, Latoya grins.
"There's so much excitement, I've seen people screaming when they come down the stairs," she says.
"Thanks for working so late guys, this is awesome," one thrilled customer tells station staff working on the ticket gate.
Station worker Latoya was excited to be on duty for the first Night Tube.
Just after midnight, Marcus Edwards, from Wimbledon, says he is "not heading home just yet," because he's off into town to meet some friends to go dancing in Piccadilly.
"Usually people are rushing to get the last train, but that won't happen now — it means they'll be able to spend more time with friends."
At 12.30am, when Oxford Circus station would normally be shutting, one of its three departures boards goes blank: there will be no more Bakerloo Line trains tonight, but the Central and Victoria lines will keep running: One train each way every 10 minutes, right through until the morning.
The Night Tube's first two lines began running on August 19; others will follow later in the year.
An hour later on the Central Line, it's hot, sticky and almost as busy as rush hour.
A girl sits on the westbound platform cradling her phone, tears staining her cheeks, as wobbly drunks prop themselves up against the wall and stare, unfocused, into the distance, awaiting the next train.
“Won't you stay for one more drink with me?
'cause your last train is never gonna leave.
You can wait forever to be free ...
or you can ride the night train with me.”
Heading east out of London, a tipsy trio of girlfriends are clutching greasy brown paper bags from McDonald's and arguing good-naturedly about their respective routes home.
"I'm definitely more drunk than I've ever been on the normal Tube," says a twenty-something guy, swinging from the overhead hand rail.
Next to me, two women debate whether 2.30am is too early to arrive wherever it is they are heading; their night is just getting started.
For others, the fun is well and truly over, they doze fitfully, green around the gills and swaying along with the movement of the train.
Plenty of passengers got a nap on their way home on the Night Tube ...
The carriage gradually empties as we head further east. By the time we reach the end of the line at 2.42am, there are just four others in the carriage, two of them asleep.
It turns out they've missed their stop after a heavy night out in town, and — like me — have to turn around and head back the way we just came; a few stops later they're almost home, after briefly getting stuck in the doors.
At Leytonstone, I meet three teenagers tripping barefoot along the platform, vertiginous heels in hand, with friends Meg Abery and Emily Smith; they've been to Faces, a nightclub famous for its appearances in reality TV show "The Only Way is Essex," to celebrate their A-level results.
"... normally we'd have had to get a £30 ($39.40) or £40 ($52.54) cab, and this is much cheaper, plus it's peace of mind for my parents."
Friends Sarah, Meg and Emily rode the Night Tube home to Essex after a late night of clubbing.
Tracey Harknett said the Night Tube was a godsend after a late-night return from overseas.
At Liverpool Street Station, groups sprawl on the floor outside the station eating junk food.
Tracey Harknett, her partner and three children have just arrived back in London after a holiday in Turkey -- thanks to the Night Tube, they're looking forward to being home in time for breakfast.
"We'd have no other way of getting home at this time. If only the Jubilee line was open, we'd be there much sooner. We're dying to get home for a bacon sarnie!"
Early starts, late finishes
Oxford Circus, one of the busiest stations on the Underground, is at the center of the Night Tube network.
By 5am, the escalators and passageways at Oxford Circus are quieter than they were a couple of hours ago, and the mood has shifted: there are still pockets of people heading home, but most passengers are just beginning their day: bleary-eyed and yawning.
Sebastian Cringaci, originally from Romania, is on a southbound Victoria line train, heading to work in East Croydon. He's already a big fan of the new service.
CNN's Becky Anderson takes a look back at the London Tube as seen in films.
"It makes a major difference to me," he explains. "This morning I got the 4.38am train, instead of getting up at 3.50am to start my shift at 6am! It will make my life much easier — on weekends at least. It means I get half an hour or three quarters of an hour extra sleep."
At the taxi rank near the station in Vauxhall, cabs are lined up waiting for their fares. Richard Amoah says business is slow, but he and his fellow drivers blame Uber, rather than the Night Tube.
It's been 150 years since the first journey on the world's first underground railway in London. Nick Glass reports.
"It's been a very quiet night," he says. "But I don't think that's because of the Tube being open — that's not impacting us, yet. It might do at a later stage."
Back across the river at Warren Street, station cleaner Hristina Duzoda is celebrating the end of her overnight shift with a breakfast of sushi, eaten in the street.
"We weren't too busy here, compared to some of the other stations, but there were lots of young people, and everyone was really happy," she says before going back inside to grab her bag.
London may officially now be a city that never sleeps, but she needs to: she's due back at work by 11pm.