The ban on flights at UK airports has been extended until 7pm Saturday night local time, after flight officials said the situation due to the cloud of volcanic ash was 'worsening'
Restrictions which had earlier been lifted on flights over Scotland, Northern Ireland and northern England were reapplied, said the National Air Traffic Services (NATS).
"Current forecasts show that the situation is worsening throughout Saturday," said NATS, which manages British airspace.
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The ban was also extended by six hours to 7:00 pm (1800 GMT).
The air authority had introduced a virtually unprecedented flight ban across all British airspace at midday (1100 GMT) Thursday, before relaxing the restrictions in Scotland, Northern Ireland and Manchester in northwest England.
Britain is one of more than 15 European countries to have introduced flight bans because of the ash cloud.
On Saturday afternoon Australian time, the ban reached Southern Eruope, with Italy announcing it was also taking the precaution.
Australians face huge delays
Meanwhile, Australian travellers face unprecedented delays because of the disruption.
Airlines warn that Europe-bound flights from Australia could be delayed up to a week by the vast cloud of volcanic ash blanketing most of the continent.
Qantas spokesman David Epstein says passengers should prepare for significant disruption with the volcanic eruption in Iceland grounding flights across Europe in the biggest air travel shutdown since World War II.
"At this stage it's highly unlikely things are going to return to normal for several days at least, and it may well be a week," Mr Epstein said on Saturday.
About 2000 Qantas customers in Asian ports are being given the option of onward flights to other destinations or flights back to Australia.
8000 Qantas customers impacted
The national carrier estimates 8000 Qantas customers have been impacted by the eruption, while about 100 international passengers stranded in Australia are being accommodated in Sydney hotels.
Mr Epstein said five daily flights usually bound for Europe on Saturday would proceed to Asian stopovers but not to onward destinations.
"It's a question of making a judgment not just when the airspace is open but when the airports are actually capable of taking our flights in and out in a way that doesn't disrupt passengers too much."
The backlog of customers would be accommodated as much as possible, Mr Epstein said, including flexibility with fares and rescheduling.
Qantas' meteorological unit tracks volcanic activity 24 hours a day, Mr Epstein said.
"It's best to put safety before schedule and where there's any question of volcanic ash being in the air we would prefer to take the safe approach rather than risk it to get flights in."
Airlines losing A$214m each day
The Air Transport Association in Geneva estimates the current cost of the eruption to major airlines at around $US200 million ($A214 million) each day.
An Emirates spokesperson said passengers were urged not to go to airports before establishing the status of their flights.
"Emirates is keeping its flying schedule under constant review and will aim to give customers as much notice as possible once more information is received from European Air Traffic Control authorities," the spokesperson said.
Singapore Airlines spokeswoman Susan Bredow told AAP all passengers stranded in Singapore would be brought home free of charge.
"We're going to bring everyone home as soon as as possible," she said.
Flights started bringing passengers back to Australia on Saturday and passengers were being re-booked with a five-day delay anticipated.
