GRETA Thunberg's high-profile "eco" crossing of the Atlantic hit choppy waters tonight when it was revealed a crew will have to FLY to New York to bring her boat back.

The Swedish climate activist, 16, is crossing the giant ocean in a racing yacht to join protests in the US and take part in a United Nations summit.

3 The Swedish climate activist is crossing the Atlantic to join protests in the US Credit: AFP or licensors

She is making the two-week voyage in the state-of-the-art 60ft Malizia II yacht - one of the fastest ocean sailing boats on the planet.

The £4m boat - skippered by Boris Herrmann - has been fitted with solar panels and underwater turbines that produce electricity on board, with the aim of making the journey zero-carbon.

However, reports in Germany have now revealed two people will have to jet out to America to return the ship to Europe.

Some news sources claimed a further two will also fly out to meet up with Greta, however those reports have yet to be confirmed.

The non-stop journey eco warrior Greta is making is - in theory - the lowest-carbon option to cross the Atlantic.

However, Team Malizia spokeswoman Holly Cova said of the flights: “We only have one boat, so they cannot easily sail over to meet them.”

Cova said the team recognises it’s “an imperfect solution” but believes offsetting the emissions by funding carbon-reducing projects elsewhere “is better than doing nothing.”

On board are Herrmann, the boat's owner Pierre Casiraghi (the grandson of Monaco's late Prince Ranier and actress Grace Kelly), Greta's father Svante and cameraman Nathan Grossman.

Before setting off from Plymouth, Thunberg accepted that solar yachts are not for everyone but says she was hoping to demonstrate there are alternatives to air travel.

“I don’t tell people what to do. People can do what they want,” she said.

Although some have slammed the teen campaigner on Twitter since news of the flights broke, her supporters are staying loyal.

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Hitting out at the critics, Andy Fish Bloke tweeted: "SHE has done more in one year of her young life to champion a cause she believes in, than anything YOU have your entire life."

Chapeau Blanc said of the news: " If that's confirmed, it might sound absurd at first. But Greta is like a politician, she's fighting with symbols.

"There are 37 MILLIONS of flights per year, 4 BILLIONS of passengers. Hopefully many will listen to Greta's message and will take the plane less often."

3 German yachtsman Boris Herrmann is at the helm of the 60ft Malizia II yacht Credit: Reuters

3 The £4m boat has been fitted with solar panels and underwater turbines that produce electricity on board Credit: AFP or licensors