Silvio Berlusconi, Italy's prime minister, has promised that the island of Lampedusa will be free of migrants in the next few days, during a visit to the Italian territory.
About 19,000 people have arrived on the tiny Mediterranean island since January, most travelling from Tunisia and Libya.
"The 'Free Lampedusa' plan began at midnight ... In 48 to 60 hours, Lampedusa will be inhabited only by the people of Lampedusa," Berlusconi told cheering residents.
About 6,000 migrants are living in makeshift shelters, many without water or toilets, outnumbering the normal population and bringing the local infrastructure close to collapse.
After weeks of complaints that went disregarded, residents stepped up their protests this week, blocking the harbour and threatening a general strike if the problem was not solved swiftly.
On Wednesday morning, five Italian ships arrived to take migrants to camps on the mainland.
With only three chemical lavatories, little access to water for washing, and growing tensions between locals and immigrants, aid organisations and charities have denounced the government for poor management of the crisis.
"It's not possible in the long term to leave 5,000 inhabitants living alongside 6,000 immigrants in such conditions," Laura Boldrini from the UN High Commission for Refugees, said.
"The situation is very tense. We cannot lose any more time," she said.
Giorgio Napolitano, Italy's president, also condemned the situation as "unacceptable".
"We must intensify transportation in order to evacuate most of the people who have arrived," he said, calling on Italian regions which may have to put up the immigrants on a temporary basis to show "cohesion and solidarity".
Migrants to the island have protested at their confinement and are also worried about where they are being taken and whether they will be free to seek employment.
"I left Tunisia because I didn't have any work. I don't know what will happen today and I'm afraid, very afraid," 21-year-old Tunisian Bechir told the AFP news agency
"No-one knows anything and they are not telling us anything. I just want to join my family in France."
Most of the arrivals since the start of the year have sailed from Tunisia, but in recent days boats have also come from Libya.
Berlusconi's visit came as another rickety boat carrying around 100 people was towed into the port and as aid organisations warned that living conditions for the migrants were untenable.
Italy has renewed its appeal for help from the European Union to deal not just with Tunisian migrants looking for a better life following the unrest in their country, but also with refugees from other parts of Africa held in detention camps in Libya.
The Italian government has previously warned thst hundreds of thousands of migrants could depart for Italy's shores if the regime of Muammar Gaddafi, the Libyan leader, falls and Gaddafi himself has threatened to send "millions" to Europe.
"These are not just economic migrants and we continue to ask Europe to take action," said Franco Frattini, Italy's foreign minister, adding that promises for "very limited European funds" were not enough.
"We have made around 18 million euros [$25m] available to Italy in 2010-2011 for repatriations, on top of 25 million euros [$35m] allocated to all member states for emergency measures," an EU spokesman rebutted on Wednesday.
Berlusconi, who had held an emergency meeting in Rome on Tuesday evening to address the immigration problem, has announced tax breaks and compensation measures for the local inhabitants of the island where the main industry is tourism.