Italy closed a large part of its airspace in the north of the country until at least the early afternoon on Sunday to counter the risk posed by volcanic ash coming from Iceland, the civil aviation authority ENAC said.
The block on flights began at 0600 GMT (0800 local time) and was expected to last until at least 1200 GMT.
The closure would not affect the airspace in the eastern part of northern Italy and the airports of Venice, Trieste and Rimini would remain open, ENAC said.
A bulletin issued on Sunday by the Volcanic Ash Advisory Centre said the ash was expected to stay over Italy until Sunday evening.
Several Spanish airports in northern Spain including Barcelona reopened on Sunday after being shut on Saturday as a precaution against the ash cloud.
The Spanish civil aviation authority said only three airports remained closed, all in the north-western region of Galicia, and that these might open from about 0900 GMT. They were Santiago, La Coruna and Vigo.
Some 24,500 flights were expected to take place in Europe on Sunday, about 500 below average for this time of year due to the ash, European air traffic agency Eurocontrol said in Brussels.
"During the day, it is expected that the area affected by the ash cloud will shrink and most of the airports that are currently closed are expected to open later," it said.
Trans-atlantic flights remain affected and are required to make significant rerouting, leading to some delays, the statement said.
"However significant numbers of cancellations have not occurred," it added.
The number of flights in Europe on Saturday totalled 22,424, about 200 below normal levels, Eurocontrol said.
The Spanish government has warned that the country's airspace could be hit again in the coming week, depending on the trajectory of the ash cloud.
Ireland expects to impose restrictions to traffic at western airports later on Sunday as ash from the Icelandic volcano drifts back over the country.
In Portugal, the airport in the country's second city, Porto, was shut until midday (1000 GMT), while the French aviation authority said some 30 flights from Paris to southern Europe were cancelled, although French skies were open.