A number of flights have resumed through several major European airports, five days after volcanic ash caused thousands of planes to be grounded across the globe.
A limited number of flights to and from Asia, North America and Europe took off on Tuesday, as airports reopened in central Europe and Scandinavia.
But the development came amid warnings of a fresh cloud of debris heading towards the continent, as Iceland's Eyjafjallajokull volcano began spewing lava and heavy ash.
Al Jazeera's David Chater, reporting from Hvolsvollur in southern Iceland, said another eruption had taken place on Tuesday.
"We are seeing a spectacular light show right now ... fresh, huge bursts of lava flowing over the rim in front of me. There is fresh volcanic activity," he said.
Britain's National Air Traffic Service (Nats) said a new ash cloud was spreading south and east towards the UK, while the European Volcanic Ash Advisory Centre (VAAC) said it may also hit Denmark and Scandinavia.
British officials said London airports were likely to remain closed for another day due to the plume, although airports in the north of the country were beginning to resume, with its first flight leaving Scotland early Tuesday morning.
Imran Khan, Al Jazeera's correspondent at Heathrow airport, said passengers had been complaining that airlines were not giving them enough information.
"There seems to be a lack of clarity from the airlines themselves. They keep saying 'keep checking', but that's all they say. And passengers are getting very frustrated".
Britain has dispatched three naval ships to rescue stranded Britons, including troops returning from Afghanistan.
The aircraft carrier HMS Ark Royal and amphibious assault ship HMS Ocean were made available for those stranded in France, while the assault ship HMS Albion was en route to northern Spain to pick up British troops.
The new wave of ash has forced aviation officials to close airports on Norway's southwestern coast, from Stavanger to Kristiansand, after authorities had
lifted air travel restrictions in most parts of Norway.
Icelandic police said there was still "considerable volcanic activity at the site and
three seemingly separate craters are still erupting".
But a statement noted that the plume was "smaller and lighter" than it had been previously, "indicating that there is not much ash in it".
Flight restrictions eased
The Eurocontrol air traffic agency in Brussels said it expected about 55 to 60 per cent of flights over Europe to go ahead on Tuesday, with around 14,000 flights scheduled to take place.
"On a normal Tuesday, we would expect between 27,000 and 28,000," the aviation body said.
"By the end of today, we expect that more than 95,000 flights in total will have been cancelled since Thursday 15 April".
In China, the first flight to northern Europe since late last week set off at 12 noon local time (04:00 GMT), and the first commercial flight bound for New York's JFK airport left from Paris.
Schiphol airport in Amsterdam has seen a number of flights depart since Monday evening, with the Dutch government approving flights under certain conditions.
Airspace has also reopened or begun to partially reopen in Sweden, Austria, Italy, France, Latvia and Lithuania.
In Germany, airspace remains officially closed until 12:00 GMT and in Denmark airspace above 5,000 metres has been opened, but flights are unable to land.
The move to ease flight restrictions came after criticism from carriers, who said test flights in recent days by airlines including KLM, Lufthansa and British Airways suggested planes could fly safely despite the ash and that the danger was exaggerated.
None of the test flights reported problems or damage.
On Monday European Union transport ministers reached a deal during a crisis video conference to divide northern European skies into three areas: a no-fly zone immediately over the ash cloud; a caution zone "with some contamination" where planes can fly subject to engine checks for damage; and an open-skies zone.
David Chater reports from Iceland as scientists struggle to make sense of volcanic activity
Peter Ramsauer, the German transport minister, said all aircraft under the "control zone" plan will be thoroughly checked once they have landed.
"Much stricter tests and checks will be applied to all planes," Ramsauer said, in hopes of gaining more data about the risk from the ash.
But critics also said the action came too late, with Giovanni Bisignani, the chief of the International Air Transport Association (Iata), calling the whole situation "a European mess".
Iata accused European governments of offering "no risk assessment, no consultation, no co-ordination, and no leadership."
But pilots urged caution.
"Mixing commercial and safety decisions risks lives," said Philip von Schoppenthau, secretary-general of the European Cockpit Association, a union representing 38,200 pilots from 36 European nations.
"Our members have many firsthand experiences of the extremely abrasive and clogging effects of such clouds," he said.