Greenpeace activists in kayaks and boats have boarded a 23,498-tonne ship in the Thames Estuary. The ship is reportedly carrying thousands of Volkswagen diesel cars bound for the UK.

A group of up to 40 activists scaled the fences at Sheerness Port, Kent, at around 8.30am local time.

Greenpeace says it will not leave the ship until the cars, meant for UK suppliers, are returned to Germany.

The protesters are hanging off the harborside brandishing a huge poster of a child wearing a gas mask with the words “Ditch Diesel.”

In a statement, Greenpeace said: “The volunteers, including many mothers, fathers and people from all walks of life, are attempting to immobilise all of the VW diesel cars by removing the keys.

“They are also lifting the bonnets and labelling the engines with messages from 8,000 people, including many car owners, calling on VW to ditch diesel.”

BREAKING: We are sending a message to @Volkswagen - stop contributing to air pollution and #DitchDieselhttps://t.co/N4P9mvsF02pic.twitter.com/ZQB5mQ10cP — Greenpeace UK (@GreenpeaceUK) September 21, 2017

Diesel vehicles cause 80% of air pollution on UK streets - yet @Volkswagen CEO says diesel has a "great future" https://t.co/N4P9mvKfRApic.twitter.com/b5CFMWWluH — Greenpeace UK (@GreenpeaceUK) September 21, 2017

Janet Barker, 38, a support worker, from Powys, Wales, and one of the volunteers taking action, said: “Diesel cars are toxic – so we’re here to block VW imports on behalf of all of the children who are the most acutely affected by the health impacts of diesel fumes.

“VW’s polluting vehicles are adding to a public health emergency harming thousands of people,” Barker said, according to the Sun.

Volunteers are trying to stop the cars from being distributed to UK dealers by removing their keys.

Bo Ruan, a Greenpeace employee, warned of the consequences of diesel emissions.

“My daughter Sephie has developed severe respiratory problems which can render her housebound for a week at a time. The wealth of evidence connecting air pollution to respiratory problems in children is now overwhelming,” he said, according to the Metro.

“Our country’s children, like Sephie, are developing real health issues across our cities made worse by air pollution.

“Unless we ditch diesel, we could end up with a whole generation of children with damaged lungs.”

Kent Police said officers are at the scene.

BREAKING: We're blocking car shipment & confiscating 1000s of @Volkswagen diesel car keys 2 years on from dieselgate https://t.co/N4P9mvsF02pic.twitter.com/tX6YneGDDY — Greenpeace UK (@GreenpeaceUK) September 21, 2017

Greenpeace want Volkswagen to stop producing diesel cars within the next two years.

The German car giant imports tens of thousands of cars in the UK every year.

The stunt marks two years since the start of the Dieselgate emissions scandal.

VW came under fire after it emerged it had rigged millions of its cars between 2008 and 2015 so they would pass stringent environmental tests while still emitting dangerous levels of pollution.

Millions of cars have been recalled by VW. Other brands, including Mercedes, BMW and Audi, have installed software upgrades to slash emissions.