British regulators imposed a flight ban from Scottish and Northern Irish airports from 7:00am (0600GMT) for 12 hours for most affected airports, warning that high ash levels could damage plane engines.

Irish authorities, who stopped flights for several hours on May 4, also closed airports progressively from 0600GMT, while saying transatlantic and other planes could still fly over at higher altitudes.

“The volcano in Iceland has expelled denser, coarser ash higher into the atmosphere,” said the Irish Aviation Authority (IAA), adding that Dublin airport would remain closed until at least mid-night (2300GMT).

Britain’s Civil Aviation Authority (CAA) added, “Forecasts show that levels of ash in the atmosphere over Scotland and Northern Ireland will exceed the concentrations that engine manufacturers have agreed are safe for operations.”

While the flight ban remained in place for the rest of May 5, the CAA said it hoped the restrictions could be lifted on May 6.