The decision was backed by other mayors in Italy's south, including those in Naples, Messina and Reggio Calabria, who all said they were ready to disobey Salvini's order and allow Aquarius to dock and disembark in their seaports, the Guardian reported.
Spanish Prime Minister Pedro Sanchez, who took office just over a week ago, has given instructions for the boat to be admitted to the eastern port of Valencia, his office said in a statement.
Speaking to the press in Milan, the deputy PM said: "Evidently raising one's voice politely pays off, something the Italian Government hadn't done in years". The proposed changes would arguably increase the pressure on Italy without ensuring a more equitable distribution of responsibility. More than 1.8 million have entered Europe since 2014.
There are an estimated 629 migrants on boat the Aquarius, including 123 unaccompanied minors and seven pregnant women.
Italy's closed its ports to the ship and said it should dock in Malta where Prime Minister Joseph Muscat insists global law determines Italy is responsible for them. "This is a European issue", he said on Twitter.
"From now on, Italy isn't alone, and we hope other European leaders follow" Spain's example, said Di Maio, who along with the League is seeking to renegotiate the EU regulations that determine which EU country is responsible for processing asylum claims. Picture taken June 9, 2018.
The MV Aquarius as migrants and refugees are rescued by the SOS Mediterranee organisation in the Mediterranean Sea, off the Libyan Coast, September 14, 2017.
Vienna possible venue for Trump-Putin summit
Another posting says he is looking forward to straightening out unfair trade deals with the G7 countries. When will this very expensive Witch Hunt Hoax ever end?
Some in Italy have offered to take in migrants. "The Mediterranean is the sea of all the countries that face it, and it (Malta) can't imagine that Italy will continue to face this giant phenomenon in solitude". "The island can not continue looking the other way when it comes to respecting worldwide conventions", read the Italian government's statement signed by Salvini and Transport Minister Danilo Toninelli.
In defiance of Salvini and the government's anti-immigrant stance, several Italian mayors have suggested they would be prepared to welcome the Aquarius into their port.
The European Union has called for action to resolve the situation. "We are talking about people".
The 77-metre ship, the Aquarius, was effectively stranded on Monday in worldwide waters in the Mediterranean, between Sicily and Malta, while its captain tried to find a secure port.
Although Spain offered safe harbour to the boat and the 629 migrants on board, the episode has raised questions about a country's legal obligations towards those rescued at sea.
Italy's new interior minister, Matteo Salvini, said on Sunday that from now on, "Italy, too, begins to say NO to the trafficking of human beings".
In another Facebook post on Monday, Salvini assailed the Sea-Watch 3, another rescue ship operating in Mediterranean waters that had to wait hours to be assigned a disembarkation port over the weekend.
Nearly a quarter of the migrant survivors hail from Sudan, the group said. But Italy can not simply expel hundreds of thousands of undocumented migrants without severe repression, and Italy doesn't yet have the agreements with many key countries of origin needed to facilitate returns.