The German-flagged Louise Michel said it was “reaching a State of Emergency” after encountering the boat 130 people as they attempted to cross the expanse dividing Europe and Africa.
“There is already one dead person on the boat. We need immediate assistance,” the crew of the 31-metre (101 feet) Louise Michel wrote on Twitter, saying other migrants had fuel burns and had been at sea for days.
Named after the 19th-century French anarchist Louise Michel, the vessel's crew of 10 had earlier rescued another 89 people from a rubber boat in distress on Thursday.
The boat was around 90 kilometres southeast of the Italian island of Lampedusa early on Saturday, according to the global ship tracking website Marine Traffic.
Thousands of people are thought to have died making the dangerous crossing across the Mediterranean to flee conflict, repression and poverty in Africa and the Middle East.
Banksy's decision to fund the high-speed boat follows a body of work by the artist that has levelled scathing judgements on Europe's halting response to the migrant crisis.
'I can't keep the money'
Painted in hot pink and white, the Louise Michel features a Banksy artwork depicting a girl in a life vest holding a heart-shaped safety buoy. The motor yacht, formerly owned by French customs, is smaller but considerably faster than other charity rescue vessels — enabling it to outrun Libyan coastguard boats, according to The Guardian newspaper.
It has 10 crew members “made up of European activists with long experience in search and rescue operations” and is captained by German human rights activist Pia Klemp, who has also captained other such rescue vessels, the paper reported.
Banksy's involvement in the rescue mission goes back to September 2019 when he sent Klemp an email.
“Hello Pia, I've read about your story in the papers. You sound like a badass,” Banksy wrote. “I am an artist from the UK and I've made some work about the migrant crisis, obviously I can't keep the money. Could you use it to buy a new boat
or something? Please let me know. Well done. Banksy.”
Klemp, who initially thought it was a joke, told the paper she believed she was chosen because of her political stance, The Guardian said.
“I don't see sea rescue as a humanitarian action, but as part of an anti-fascist fight,” she told the paper.
The crew with diverse backgrounds “all identify as anti-racist and anti-fascist activists advocating for radical political change,” The Guardian said.
A spokesman for Burriana's port confirmed that the Louise Michel docked there on June 23 and left on August 18.
“During this time, they have been repairing and preparing the boat but they did it by themselves, they did not use the port services”, he told AFP.
About Banksy, “if he has been here, he came incognito,” the official said.
The Louise Michel left Burriana on August 18 “under the strictest secrecy”, The Guardian reported.
Early this month, humanitarian organisations said they would resume migrant rescues in the Mediterranean Sea where none have operated since the Ocean Viking docked in Italy in early July.
Before the Ocean Viking's last mission, rescue operations in the Mediterranean had been suspended for months due to the global coronavirus pandemic.
More than 100,000 migrants tried to cross the Mediterranean last year from north Africa with more than 1,200 dying in the attempt, according to the International Organization for Migration.