One of the biggest single-day rescue operations to date appeared to have been concluded without any reports of casualties.

Two navy ships, the Cigala Fulgosi and the Vega, picked up, respectively, 507 and 432 migrants from two wooden boats in danger of sinking just off Libya, the navy said.

The coastguard said its patrol boats had boarded a total of just under 1,000 people from various unseaworthy fishing boats and inflatables that had left Libya overnight Friday-Saturday.

At least another 1,000 rescued migrants and refugees were reported to be headed for Italian ports on other boats as the wave of new arrivals triggered increasingly virulent attacks on centre-left Prime Minister Matteo Renzi's handling of the migration crisis.

"This must a joke. We are using our own forces to do the people smugglers' business for them and ensure we are invaded," said Maurizio Gasparri, a senator for Silvio Berlusconi's centre-right Forza Italia party.