London, England (CNN) -- London's two major airports were closed Monday as a cloud of ash from a volcano in Iceland moved east into England, British air authorities said.
All flights into and out of Heathrow and Gatwick airports have been canceled for a six-hour period beginning early Monday, airport officials said.
The affected flights are those scheduled between 1 a.m. (8 p.m. Sunday ET) and 7 a.m. (2 a.m. ET).
The Monday cancellations were the latest in a round of weekend closures of airports across the United Kingdom and into continental Europe.
Amsterdam's Schipol Airport announced it would be closed Monday from 6 a.m. to 2 p.m. (midnight Sunday to 8 a.m. ET), according to an airport spokeswoman, who said officials were waiting on guidance from air authorities to decide when flights will resume.
Birmingham, Norwich Manchester and Liverpool airports were closed on Sunday evening, controllers announced.
In addition, Dublin's airport closed overnight, the Irish Aviation Authority said Sunday, and will remain closed until at least 9 a.m. (4 a.m.) Monday. International flights through Irish airspace will not be affected, it said.
Waterford airport was set to close at 11 p.m. (6 p.m.) and four other Irish airports remain closed. Shannon, Cork and Kerry airports are open.
Flights were also stopped at all airports in Northern Ireland, as well as the British airports at Ronaldsway, Prestwick, Carlisle, Doncaster, Humberside, Leeds Bradford and East Midlands.
Some Scottish island airports also shut down, including Campbeltown, Islay and Barra, the air traffic control agency NATS announced. And if the volcano continues to erupt at current levels and weather conditions prevail, air travel in Britain could be disrupted between Sunday and Tuesday.
"The government is carefully monitoring this situation and the safety of passengers will remain our paramount concern," said Philip Hammond, transport secretary.
The department said predictions remain fluid, urging passengers to check with airlines before taking any action. British Airways said it would notify passengers of potential disruptions on its website.
"There is a distinct possibility of some disruption from the ash cloud over the southeast of England, but it is too early to tell if this will extend as far as Heathrow or Gatwick yet," a BA spokesman told CNN.
Volcanic ash had forced the closing of Iceland's main airport Friday but it reopened at midnight and operated normally on Saturday.
Earlier in the week, traffic was shut down in airports from central Spain to the Canary Islands off the coast of Africa.
The problems began in mid-April, when the volcano beneath the Eyjafjallajokull glacier in southern Iceland erupted and sent a cloud of ash into the atmosphere, disrupting international travel for several days.
There's no way to know how long the volcano will continue spewing ash into the air, Georgia Tech scientist Josef Dufek told CNN.
"It could go on another year," he said, noting that an eruption lasted that long in 1820.
Volcanic ash can be a serious hazard to aircraft, reducing visibility, damaging flight controls and ultimately causing jet engines to fail.
British ministers agreed Saturday that five-day ash-prediction charts would now be made available to airlines, other transport providers and the public on the Met Office website. Previously, only 18-hour forecasts had been available.
CNN's Caroline Paterson contributed to this report.