Restrictions currently in place across UK controlled airspace will stay until at least 1200 GMT on Saturday, officials say
Ryanair cancels all flights in northern Europe until 1300 GMT on Monday
British Airways cancels all flights in and out of London airports on Saturday
Hungary said it would shut its airspace from 1900 (1700 GMT)
Switzerland said it would follow suit from midnight (2200 GMT)
Romania said it would close airspace over the north-west of the country from 0300 (0000 GMT) on Saturday
The UK's National Air Traffic Service (Nats) said trans-Atlantic flights would be able to operate to and from the re-opened airspace, but stressed this did not mean all such flights would resume.
The disruption has affected hundreds of thousands of travellers since Wednesday when the Eyjafjallajokull volcano began erupting for the second time in a month, hurling a plume of ash 11km (seven miles) into the atmosphere.
The cancellations also threaten to affect the funeral on Sunday of Polish President Lech Kaczynski, who was killed in a plane crash last Saturday, with the attendance of many world leaders now uncertain.
The European air traffic agency Eurocontrol said the ensuing chaos was worse on Friday than the previous day, and warned of "significant disruption" to air traffic on Saturday.
With the volcanic ash able to bring down aircraft, some 60% of flights in Europe have been grounded, and more than half of trans-Atlantic flights cancelled, the European air traffic agency, Eurocontrol, said.
At a news conference in Brussels on Friday afternoon, the agency warned travellers to expect significant disruption on Saturday, as the ash moves south and east.
Europe's busiest airports, including London's Heathrow, Frankfurt and Charles de Gaulle in Paris, are among dozens affected, with a succession of countries announcing further planned shutdowns.
'Worse than 9/11'
"In terms of closure of airspace, this is worse than after 9/11," a spokesman for Britain's aviation regulator, the Civil Aviation Authority (CAA) said.
"The disruption is probably larger than anything we've seen."
Icelandic Met Office's Matthew Roberts: 'The ash cloud reached 8km high'
In addition to the impact on commuters, the grounding of thousands of flights has cost airlines about $200m a day, according to the International Air Transport Association.
But the chaos has benefited rail, bus and ferry tour operators, who have laid on extra services, and many hotels have filled up with stranded travellers.
We can actually smell sulphur in the air here now from the volcano cloud
Eurostar said its train services between London and Paris and Brussels were sold out on Friday, and urged people not to come to St Pancras station in London to look for tickets.
As the volcanic ash drifted south, Sweden began reopening its northern airspace. Officials said restrictions further south would be lifted gradually on Friday. Norway allowed some flights in the north as well.
The Irish Republic also opened its airspace apart from a block off the south coast, putting Dublin, Shannon and Cork airports back into operation.
Fresh flooding meanwhile has hit the area around Eyjafjallajokull volcano, as hot gases melted the glacier.
Hundreds of people were evacuated from their homes as water carried pieces of ice reportedly the size of small houses down the mountain. A road along the flooded Markarfljot river was also cut in several places.
Matthew Roberts, from the Icelandic Met Office, told the BBC the eruption was weakening and it was no longer producing as much ash.
MONITORING ASH CLOUD FLIGHT DISRUPTION
Flightradar24.com, which monitors aircraft in flight, shows the impact of the ash cloud as the area affected by closures expands south across Europe
British health officials said the effects of the ash on people with existing respiratory conditions were "likely to be short term".
The last eruption of the Eyjafjallajokull volcano was on 20 March, when a 0.5km-long fissure opened up on the eastern side of the glacier at the Fimmvoerduhals Pass. The eruption prior to that started in 1821 - and continued for two years.
Iceland lies on the Mid-Atlantic Ridge, the highly volatile boundary between the Eurasian and North American continental plates.
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