Aviation officials in Europe say the closure of airspace there is likely to worsen, as volcanic ash continues to spread over the continent.
Many countries have closures in place until at least Sunday evening, and France says the airports around Paris will be shut until Monday (local time) at the earliest, while Britain extended its ban on commercial flights until 0100 on Monday, local time.
An estimated three quarters of European flights on Saturday were grounded - a total of nearly 17,000 flights.
The disruption is now said to be worse than after the 9/11 terrorist attacks in the United States.
The head of meteorology and research at Britain's national weather service, Brian Golding, says the volcano seems to have been re-invigorated.
Mr Golding says it's not known how long the volcano will keep erupting but that a new wave of ash is entering the windstream.
Meteorologists say the winds blowing the ash cloud from Iceland across Europe will continue in the same direction for at least two days and could go on until the middle of next week.
The ash has been slowly spreading over much of the continent, forcing the biggest air travel shutdown since the Second World War and stranding millions of passengers around the world.
Air New Zealand's international general manager, Ed Sims, says the situation is worsening because the volcano is erupting continuously, and Brian Flynn of the air safety body Eurocontrol sees no signs of an early improvement.
With most of Europe's airspace deemed unsafe for planes, 22 countries have announced full or partial aviation restrictions and most major international airports in Europe are closed.
Airlines test planes
Dutch and German airlines have carried out test flights and say their planes appear undamaged by the volcanic ash.
The test flights are taking place at lower altitude than usual.
The Dutch airline KLM says if further examinations show its test flight to have been successful, it hopes to fly seven planes back from Germany to Amsterdam and get permission to restart some of its operations.
Volcanic ash has an abrasive effect and can strip off vital aerodynamic surfaces and paralyse an aircraft engine, while aircraft avionics and electronics can also be damaged.
Passengers offered free flights home
Thousands of flights have been cancelled, leaving travellers stranded across the world. With thousands stuck at Singapore's Changi Airport and accommodation in the city completely full, Singapore Airlines is barring passengers embarking on international flights if their final destination is in parts of Europe - and is offering them a free ride back home.
Qantas is also offering to fly passengers stranded in Asian destinations free to Australia.
Among the latest countries to announce restrictions to their airspace are Italy, Hungary, Switzerland and Romania.
Cloud contains glass, sand and rock particles
The cloud of ash is drifting across an area including Britain, Scandinavia, Poland, northern France and Austria, towards Russia at about 40km/h. Its mixture of glass, sand and rock particles could be catastrophic to aircraft.
A British scientist allowed to fly through the ash cloud says normal planes wouldn't be able to see the particles and the danger is real.
The disruption began on Wednesday when the Eyjafjallajokull volcano began erupting for the second time in a month.
