Berlin ( CNN ) -- The peak of a cloud of volcanic ash that forced the cancellation of hundreds of flights has passed , Iceland 's prime minister said Wednesday . `` The worst is over , '' Prime Minister Johanna Siguroardottir said . `` And now the clean-up can begin . Our geoscientists say that the eruption is waning day by day and that the problems arising in our neighboring countries as a result of volcanic ash should be resolved quickly . '' According to the Icelandic Meteorological Office , the eruption of the Grimsvotn volcano `` paused '' at 2:40 a.m. Wednesday ( 10:40 p.m. Tuesday ET ) , meaning it was not erupting at the moment . The agency warned , however , that it could begin again , and that only after three months with no eruptions will the volcano be considered dormant . Meanwhile , some German airports were reopened Wednesday after cancellations due to the cloud of volcanic ash . Bremen has reopened and Hamburg is allowing takeoffs and landings , according to Deutsche Flugsicherung , the German aviation safety agency . Airports in Berlin will resume flights at 2 p.m. local time ( 8 a.m . ET ) . The closures affected at least 600 flights in Germany , authorities said . Poland could be affected later in the day , the European air traffic control agency Eurocontrol said . PrzemysBaw Przybylski , the spokesman for the Chopin airport in Warsaw , said as of Wednesday afternoon flights into Warsaw were still being accepted . But the ash cloud is dissipating and much of the rest of European air travel is expected to be running normally Wednesday , the agency said . A portion of the ash from Saturday 's eruption in Iceland had spread over Britain by Tuesday afternoon , with the cloud reaching London 's Heathrow airport around lunchtime , a computer model indicated . Eurocontrol reported about 500 flights in British airspace were canceled Tuesday . Heathrow alone normally operates about 1,300 flights a day , and Europe as a whole has about 29,000 daily , according to Eurocontrol . The Grimsvotn eruption came about 13 months after Iceland 's Eyjafjallajokull volcano belched smoke and ash into the skies over the continent , forcing the cancellation of thousands of flights per day at the peak of the problem . The ash can be a serious hazard to aircraft , reducing visibility , damaging flight controls and ultimately causing jet engines to fail . Grimsvotn 's eruption was more than 10 times larger and put more ash into the air in 36 hours than last year 's burst did in a month , University of Iceland geophysicist Magnus Tumi Gudmundsson told CNN Tuesday -- but the main eruption is now over , he said . Disruptions from the larger eruption are likely to be smaller than they were in 2010 , said Gillian Foulger , a geophysicist at Britain 's Durham University . Most of the ash is blowing northwest , toward sparsely populated Greenland , and the European aviation industry collected valuable safety data during last year 's event . `` It 's much better able to set the safety thresholds accurately , so I think things are probably going to turn out very well for us , '' Foulger said . Airlines have been making the case that it is safe to fly through ash clouds of medium density , Britain 's Civil Aviation Authority said Tuesday . Carriers including British Airways , Virgin and EasyJet are now free to fly through clouds of up to 4,000 micrograms per cubic meter if they feel it is safe to do so , Richard Taylor of the CAA told CNN . Grimsvotn lies beneath Iceland 's Vatnajokull glacier , a sheet of ice more than three times the size of the U.S. state of Rhode Island -- larger than any on mainland Europe . Grimsvotn is the country 's most active volcano and last erupted in 2004 , according to the Icelandic Meteorological Office . `` If history is any guide , we expect the next eruption to be in five to six years , '' said the agency 's Jakobsdottir on Wednesday . In 1783 , a 16.7-mile fissure system from the volcano produced the world 's largest known historical lava flow over a seven-month period , damaging crops and livestock , according to the Smithsonian National Museum of Natural History . A resulting famine led to the death of one-fifth of Iceland 's population , according to the museum . CNN 's Frederik Pleitgen , Ayesha Durgahee and Adam Reiss contributed to this report .
NEW : Grimsvotn 's eruption has `` paused , '' the Icelandic Meteorological Office says . Poland could be affected later Wednesday . A cloud of volcanic ash from Iceland is affecting European air travel . Score: 6