Brian Flynn, the head of network operations at Eurocontrol, said up to 250 flights had already been cancelled Tuesday.
Norwegian airport operator Avinor said ash from the Grimsvotn volcano has disrupted traffic in and out of Stavanger and Karmoey airports in western Norway. Ash was expected to reach southern Norway later Tuesday.
In Denmark, authorities said airspace was closed in the northwestern part of the country, while ash was causing some delays and cancellations in Copenhagen.
On Monday, flights in and out of Scotland were heavily disrupted by Grimsvotn's ash, and thousands of travellers were affected by the disruption.
The BBC reported Tuesday that the ash that had reached northern Scotland was expected to reach Wales, northern England and Northern Ireland by the middle of the day.
Much of the U.K. was expected to be affected by the end of Tuesday, the broadcaster reported.
The ash cloud caused U.S. President Barack Obama to cut short his visit to Ireland on Monday.
In April 2010, another volcanic eruption grounded planes across northern Europe for five days, stranding some 10 million travellers. Thousands of flights were grounded and airlines lost millions of dollars after the Eyjafjallajokull volcano blew.
Because of what happened last year, British government officials say they are now better prepared to avoid a mass grounding of planes under similar circumstances with new guidelines that can determine which airline fleets are safe enough to fly through low- and medium-density ash clouds.
with files from The Associated Press