She was Time magazine's person of the year and is admired all over the world, but that didn't stop Germany's national rail company from throwing shade at Swedish teen Greta Thunberg on Twitter this weekend. Have the wheels come off Deutsche Bahn's PR strategy?

Berlin (dpa) - It's a scenario most German train travellers are familiar with: The train is totally overcrowded, all the seats are occupied and you have no option but to sit on the floor. Even if you are Greta Thunberg.

The Swedish teen climate activist found herself in this position on Sunday as she embarked on her return journey from the UN Climate Conference in Madrid. No big deal in itself - until she posted a photo from the trip on Twitter.

The photo shows Greta sitting on the floor of a train, surrounded by luggage, staring thoughtfully out of the window. It's light outside, and behind her the word "comfort" can be seen on a sign.

The caption says she is travelling on "overcrowded trains through Germany" and finally on her way home.

The photo caused an outcry on Twitter, where Greta has 3.6 million followers. Many of them reacted in good humour - calling out Deutsche Bahn for delays and overcrowding is, after all, a popular pastime on German social media.

"Prepare yourself for delays," one user wrote.

"Welcome to Germany, the public transport here is chaos," warned another.

"A true Deutsche Bahn experience," a third chimed in.

This was all rather awkward for Deutsche Bahn, which had earlier on Sunday announced a new timetable with more journeys and more trains - the point being to make it more attractive to travel in a climate-friendly manner.

The state-owned company plays an important role in the government's climate change programme, with billions of cash flowing into its coffers as a result. And yet, there are still major problems with delays and a lack of seats.

Deutsche Bahn responded to Greta's photo by saying that she had a first-class seat between Kassel and Hamburg - so the majority of the journey between Frankfurt and Hamburg, which takes about four hours according to the timetable.

The company wrote on Twitter that it was pleased to see Greta was supporting "us rail workers" in the fight against climate change.

"We were very happy that you were with us in the ICE 74 on Saturday. And that with 100 per cent green electricity."

And then: "It would have been even better if you had also reported how friendly and competent our staff were in looking after you in your first-class seat."

This was followed by comments from other social media users that Greta had misled the public with her photo. She responded by explaining that her train from Basel had been cancelled, so she had been forced to sit on the floor in two separate trains. In Goettingen, she had finally got a seat.

"This is no problem of course and I never said it was," the teen wrote.

She even saw it as a good thing: "Overcrowded trains is a great sign because it means the demand for train travel is high!"

A happy, ending, then? For Greta, it is at least an end to four and a half months away from her home in Sweden. It was the beginning of August when she left her home to travel to Lausanne for an international Fridays for Future climate conference.

From there, she went on to Plymouth, where she boarded a yacht to take her across the Atlantic to New York - not without criticism that some members of her team took flights.

The 16-year-old refuses to fly as part of her efforts to combat climate change.

From New York, where she spoke at a UN climate summit, Greta attended other engagements in Montreal, Canada, and then travelled across the US to Los Angeles. She was supposed to travel on to another conference in Santiago, Chile, which was cancelled due to unrest in the country.

But Madrid stepped in, and Greta began her journey back to Europe. She hitched a lift on a catamaran from Virginia to Lisbon, arriving in Madrid just in time for climate protests there on December 6.

At the conference itself, she complained that politicians from the participating countries lacked any sense of the urgency of the crisis.

On the way back to Sweden on Friday, she made a quick stop in Turin, Italy. After making a speech to climate demonstrators there, she told journalists she needed a break and would be heading back to Sweden for Christmas.

The only member of her family to accompany on her big journey was her father Svante. Back home, she will be reunited with her mother, sister and the two family dogs. And no doubt there will be no more long train journeys - at least for now.