Supporters have rallied around the 31-year-old German captain who faces up to 10 years in prison.
Sea-Watch 3 skipper Carola Rackete, who risks jail time for forcing her way into Italy's Lampedusa port with 40 rescued migrants, has defended her act of "disobedience", saying she was compelled to avert a human tragedy.
"It wasn't an act of violence, but only one of disobedience," Rackete told the Italian daily Corriere della Sera in an interview published Sunday as funds poured in for her legal battles.
The 31-year-old German captain is accused of putting a military speedboat and the safety of its occupants at risk in the incident on Saturday.
No one was hurt.
"The situation was desperate," she said. "My goal was only to bring exhausted and desperate people to shore.
"My intention was not to put anyone in danger. I already apologised, and I reiterate my apology," she told Corriere.
Her father Ekkehart Rackete told newspaper group RND he expected her to "be freed under conditions or bail until the beginning of the trial."
After speaking by phone late Saturday, Rackete described his daughter as "jolly and in good spirits.
The migrants were allowed to disembark at Lampedusa and taken to a reception centre as they prepared to travel to either France, where the interior ministry said it would take in 10, or to Germany, Finland, Luxembourg or Portugal.
The Italian coast guard then anchored the rescue ship just off the coast.
Meanwhile, Italian police and coast guard rescued 55 other migrants on Sunday, including four infants and three pregnant women in the same area, the Spanish group Proactiva Open Arms and Italian media said
Proactiva Open Arms said it had identified a fishing boat that had left Libya with 40 more migrants, while Italian media said later there were 55 people on board.
They were picked up by the group and passed to a police speedboat near Lampedusa, which was to take them to Sicily but which in fact transferred 11 who required medical assistance to a coast guard ship.
Rackete was placed under house arrest and is expected to appear before a judge early this week in the southern town of Agrigente to face charges of abetting illegal immigration and forcing her way past a military vessel that tried to block the Sea-Watch.
The latter crime is punishable by three to 10 years in jail.
Her arrest sparked a fundraising appeal by two prominent German TV stars, who had raised some 620,000 euros (A$1,004,000) by Sunday evening.
Another campaign launched on Facebook by an Italian activist has so far collected some 412,000 euros -- making more than one million euros (A$1.62 million).
Comedian Jan Boehmermann, who launched the German campaign with show host Klaas Heufer-Umlauf, said in a video posted on YouTube: "We are convinced that someone who saves lives is not a criminal. Anyone who thinks otherwise is simply wrong."
The dreadlocked Rackete has become a leftwing hero in Italy for challenging far-right Interior Minister Matteo Salvini's "closed-ports" policy.
"I didn't have the right to obey," she argued. "They were asking me to take them (the migrants) back to Libya. From a legal standpoint, these were people fleeing a country at war (and) the law bars you from taking them back there."
The head of the NGO that operates the ship, Johannes Bayer, said Sea-Watch was "proud of our captain".
Boehmermann accused Salvini of "abusing rescuers... in order to turn the mood against refugees, against the EU, and for an inhumane politics."
Salvini welcomed Rackete's arrest.
"Mission accomplished," he tweeted. "Law-breaking captain arrested. Pirate ship seized, maximum fine for foreign NGO."
German President Frank-Walter Steinmeier criticised Italian authorities in an interview with the public broadcaster ZDF.
Steinmeier told ZDF that as Italy is a founding member of the European Union, "we should expect a country like Italy to deal with such a case differently."
He also called for Europe to "play a stronger role" in resolving the migrant crisis.
Although the number of migrants crossing from Tunisia and Libya has fallen sharply from a surge in 2014-2017, they have not stopped altogether.