Britain said it would ease no-fly decrees for London's major airports on Monday because a volcanic ash cloud had shifted, lessening the threat of large-scale travel disruption in Europe at the start of the working week.
But with major Irish and Dutch airports shut, there were still echoes of last month when the same Icelandic volcano's ash prompted a number of European countries to close their airspaces for nearly a week and travel chaos ensued in Europe and beyond.
Britain had ordered the closure of London's Heathrow airport, Europe's busiest, and Gatwick to the south of the capital from 1 am (0000 GMT) to 7 am (0600 GMT) on Monday. Other parts of British airspace were shut at the weekend.
Early on Monday morning, the National Air Traffic Service (NATS) said conditions had changed and that Heathrow and Gatwick could reopen subject to restrictions but that much of Britain would remain under no-fly orders.
"Heathrow and Gatwick airports will be clear of the no-fly zone. However, restrictions will have to be applied due to their close proximity to the no-fly zone," NATS said in a statememt on its website.
Airports in Amsterdam and Rotterdam would be closed for at least eight hours from 6 a.m. (0400 GMT) on Monday, Dutch state television reported.
Other Dutch airports would not be affected, said the television, but as Amsterdam and Rotterdam were the country's two main airports the closures would effectively bring most air traffic in and out of the Netherlands to a standstill.
Amsterdam Schiphol is Europe's third-largest cargo airport and fifth-largest passenger hub.
In a statement on its website, Dutch airline KLM said: "We are currently working on a diversion plan for all affected flights to Amsterdam."
More than 100,000 flights were cancelled across Europe last month because of the volcanic ash forming a cloud over the continent.
Millions of people were stranded and airlines, already battered by the global economic downturn, lost $1.7 billion, the International Air Transport Association has said.
At the weekend, North Atlantic flights through Irish-controlled airspace were unaffected by the latest cloud of ash, with Shannon -- an important stopover for flights to and from the United States -- remaining open.
But information notices at Schipol airport on Monday showed some flights from the United States had been cancelled.
The volcano under the Eyjafjallajokull glacier in Iceland has been erupting with no sign of the explosive activity about to end and the ash plume has reached heights of 25,000 feet (7,620 metres), according to Britain's Meteorological Office.
"The ash cloud is expected to clear the UK during Tuesday as southwesterly winds become established during Monday," it said.
Volcanic ash contains tiny particles of glass and pulverised rock that can damage engines and airframes.
In 1982 a British Airways jumbo jet lost power in all its engines when it flew into an ash cloud over Indonesia, gliding towards the ground before it was able to restart its engines.
The incident prompted the aviation industry to rethink the way it prepared for ash clouds.
Railway companies laid on extra trains to cope with increased passenger levels resulting from the closure of airports.
Channel tunnel rail operator Eurostar said an extra 3,500 seats would be available for passengers between London and Paris.
British rail firm Virgin Trains said it would provide an extra 7,000 seats on Monday, mainly on the Birmingham to Glasgow and Edinburgh, and London to Glasgow routes.