The non-binding proposals were sent in writing to investment bank Mediobanca, a source familiar with the matter said. The bank is playing an advisory role in state-orchestrated efforts to assemble a consortium of investors for Alitalia.

Mediobanca's client, state railways firm Ferrovie dello Stato, has taken the lead in trying to assemble the consortium and has already lined up U.S. carrier Delta and the finance ministry as partners, but other investors are wanted.

Atlantia said last week it would look into the possibility of buying a stake in Alitalia.

Mediobanca has also received non-binding proposals from infrastructure group Toto Holding, Lazio soccer club chairman Claudio Lotito and Colombian airline Avianca, the source said.

On Sunday night, Deputy Prime Minister Luigi Di Maio confirmed the new expressions of interest and said he hoped the most ambitious proposals would win out.

"We need a new Alitalia to contribute to tourism in the country, taking tourists from all over the world on long-range routes and bringing them into the world's most beautiful country -- Italy," Di Maio said in comments he posted on Facebook.

Atlantia did not immediately respond to a phone call seeking comment.

A source familiar with Toto's position confirmed that it had submitted a non-binding proposal but did not elaborate.

Ferrovie's board will meet on Monday to evaluate the proposals and inform Rome of the potential consortium. The government, which has been propping up Alitalia with bridging finance, had set Monday as a deadline for investors.

From Monday, binding offers and an industrial plan for Alitalia are expected to be finalised in no fewer than 15 days, financial daily Il Sole 24 Ore reported on Sunday.

(Reporting by Giulio Piovaccari; Editing by Mark Bendeich)