The disruption to travellers is not expected to reach that caused by last year's volcanic eruption The airspace over Berlin and Hanover could also be affected.
Air traffic in Norway and Denmark has been disrupted but flights were expected to resume across the UK after some airspace in the north was closed.
Services in and out of Scotland, Northern Ireland and northern England had been badly hit, with about 500 flights cancelled across Europe.
Europe's air traffic controller Eurocontrol said there was a strong possibility the ash cloud would travel over parts of Denmark, Norway and Sweden but the impact on flights would probably be limited.
Germany's transport authorities have taken a tough view on the potential dangers posed by the ash, says the BBC's Stephen Evans in Berlin.
There has been no outright criticism of the decision from German airlines, but there is unease in the industry that Germany's rules regarding flying through volcanic ash are different from the rest of Europe, our correspondent says.
The head of the country's airport organisation said Europe-wide rules were needed.
France's civil aviation authority has said it expects very little disruption to air traffic and was not expecting to close any of the country's airspace.
Larger particles Britain's weather service said the concentration of volcanic ash in UK airspace would decrease significantly over the course of Wednesday.
But the Met Office said that if Grimsvotn volcano continued to erupt at "current variables", much of the country could be affected by ash on Friday, with flights being potentially disrupted.
The volcano began erupting last Saturday, sending clouds of ash high into the air.Experts say the eruption is on a different scale to that of the Eyjafjallajokull volcano last year, when millions of travellers were stranded amid concerns about the damage volcanic ash could cause to aircraft engines.
European Union transport commissioner Siim Kallas said: "We do not at this stage anticipate widespread airspace closure and prolonged disruption like we saw last year."
The ash particles from Grimsvotn are larger than those from Eyjafjallajokull, and so fall to the ground more quickly.
A forecaster at Iceland's meteorological service said Grimsvotn was producing less ash on Tuesday and the plume had decreased in height to about 5,000m (16,400ft).
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