Flights across Europe are expected to return to "100 percent" on Thursday - seven days after ash from an Icelandic volcano forced the shutdown of airspace and stranded thousands of passengers around the world, the air traffic agency Eurocontrol said.

Eurocontrol said in a statement it expected 22,500 flights, or 80 percent, to take place on Wednesday, compared with about 28,000 that would normally be scheduled.

It added almost all of European airspace below 20,000 feet was available, with restrictions in some areas such as Finland and parts of northern Scotland.

Its latest advisory for Thursday morning shows the ash cloud restricted to the north Atlantic between Iceland and Norway and Scotland.

At its peak, the crisis affected 1.2 million passengers a day and 29 percent of all global aviation, according to the International Air Transport Association.

It was the worst disruption of air traffic since the September 11 terrorist attacks in the United States in 2001. Following those attacks, the United States closed its air space for three days, forcing Europe to postpone all transatlantic flights.

In addition to clearing a massive backlog of passengers and cargo, airlines now face financial headaches as well as logistical ones.

The International Air Transport Association estimated Wednesday that the Icelandic volcano crisis cost airlines more than USD 1.7 B in lost revenue through Tuesday. Between Saturday and Monday, when disruptions were greatest, IATA said lost revenues reached USD 400 M each day.

The crisis began after the volcano beneath the Eyjafjallajokull glacier erupted Wednesday and sent a cloud of ash into the atmosphere. By the next day that cloud had reached Europe, where authorities quickly closed the airspace over safety fears.