"The invasion of one million, 1.5 million refugees would bring any country to its knees," Maroni said following a meeting with his European counterparts in Brussels on Thursday.
Warning of a "catastrophic humanitarian emergency", he insisted that Italy "can't be left to deal with this on its own".
He requested the creation of a European aid fund to help countries likely to receive large numbers of migrants, notably Cyprus, France, Greece, Italy, Malta and Spain.
The proposal was rejected by other EU ministers, who accused Italy of exaggerating.
Belgium's Interior Minister Melchior Wathelet said the figures Maroni cited were "crazy", while European Commissioner for Home Affairs Cecilia Malström said it was "too early" to talk about an influx of refugees from Libya.
Europe is not the only destination for Libyan refugees. Almost 20,000 people - Tunisians, Egyptians, Chinese and Libyans - have crossed into neighouring Tunisia via the Ras Adjir border point since Monday, according to a Tunis official.
Many of the hundreds of thousands of migrant workers in Libya, most of them from sub-Saharan Africa, will not be able to afford to travel to border crossings and may remain trapped in the country, the International Organisation for Migration has warned.