European air traffic controllers said on Sunday it expected the ash cloud from an Icelandic volcano to "shrink," allowing airports in Italy to reopen later in the day.

"Most of the airports that are currently closed are expected to open later," Brussels-based coordinators Eurocontrol said, having highlighted closures in northern Italy in particular.

However, Irish aviation authorities said they were expecting closures there later in the day.

A Eurocontrol statement said the authority expected around 500 less flights to take to the European skies than average for a Sunday at this time of year, with ash eruptions "still substantially affecting European airspace."

Flight cancellations were reported on Sunday in France, Italy and Portugal.

However, controllers said airports around Milan would reopen around midday, with Pisa and Florence likely to follow suit.

French authorities said cancellations there affected Nice, the nearest international airport to Cannes which is expecting advance arrivals among thousands of visitors for its flagship international film festival.

Transatlantic flights in particular are having to undergo "significant re-routing," leading to delays, but Eurocontrol stressed that "significant numbers of cancellations have not occurred."

The Eyjafjoell volcano began erupting on April 14, provoking widespread travel chaos with airspace closed over several European nations for a week because of fears the ash would damage aircraft engines with fatal results.

It was the biggest shutdown of European skies since World War II, with more than 100,000 flights cancelled and eight million passengers affected. The airline industry said it lost some 2.5 billion euros.

The volcano began fresh and intensive ash eruptions overnight Thursday.