Greta Thunberg's Gaza-bound "Freedom Flotilla" boat has caught fire after a "drone attack" off the coast of north Africa, activists have said.

The flotilla's Portuguese-flagged "Family Boat" was hit in a "drone strike" at around midnight, UK time, according to fellow sailor Yasemin Acar.

"The Family boat has been officially attacked - a drone came right above it, released a bomb and it exploded and the boat was on fire," Ms Acar said.

PICTURED: Grainy footage appears to show a fire burning on the rear of the 'Family Boat'

"Everyone on that boat is ok. The fire is out."

The pro-Palestine demonstrator then swiftly labelled the "drone strike" an "attack against Gaza".

"They have bombed a boat with civilians on it in Tunisian territory," she fumed.

"This is an attack against Gaza because they don't want us there. So we need you to mobilise. Let's not stay quiet."

In another furious Instagram post, she added: "Zionist entity committing crimes in Tunisian territory."

The Global Sumud Flotilla, organising the activists' summer journey to the Middle East, said in a statement: "'The Global Sumud Flotilla confirms that one of the main boats, known as the 'Family Boat' - that was carrying GSF Steering Committee members - was struck by what is suspected to be a drone.

"The boat was under the Portuguese flag and all passengers and crew are safe.

"An investigation is currently underway and when more information is available it will be released immediately.

"Acts of aggression aimed at intimidating and derailing our mission will not deter us. Our peaceful mission to break the siege on Gaza and stand in solidarity with its people continues with determination and resolve."

Ms Thunberg's fleet left Spain just days ago as part of the self-proclaimed "largest solidarity mission" in history.

It is her second attempt to reach the Gaza Strip this year, after earlier sailing alongside 11 other activists before they were intercepted by Israeli authorities 115 miles west of the territory.

She claimed they were "kidnapped on international waters" - but Israel confirmed they were given water and sandwiches before being escorted to the port of Ashdod.

This time, Israel has vowed to throw the Swedish eco-activist in "terrorist-level" conditions in the Ktzi'ot and Damon detention centre for females, according to one of the country's biggest newspapers, Israel Hayom.