Hobart (Australia) 'Mercury' newspaper - Wednesday 27 September (local time) RUAPEHU KEEPS NZ ON LEVEL FOUR ALERT Wellington - AP CIVIL defence officials yesterday maintained a high alert fearing a massive volcanic eruption at Mount Ruapehu, which is coughing up red-hot boulders the size of cars. But officials said the danger zone is limited to the mountain itself, and no communities are in danger. Belching steam 19 kilometres high and spewing ash, the 2740-metre Mount Ruapehu could become the nation's biggest volcanic eruption in 50 years, scientists said. Authorities have diverted air traffic, cancelled train services past the volcano, closed the highway around its base and shut ski fields on its slopes. The volcano quieted down overnight, said Ruapehu District Council chief executive Cliff Houston, who chaired a civil defence meeting yesterday. But a "level four" alert remains in place, indicating accelerated volcano unrest with a large-scale eruption imminent. Civil Defence officials warned people living within 100 kilometres downwind to expect heavy ash falls. "Luckily the ash is going right over the top of farmers on the eastern side of the mountain and is heading off to Hawke's Bay," Ministry of Agriculture and Fisheries livestock officer Geoff Cochrane said. "The forecast is for four days of rain in the Ruapehu area and, if there is any ash on the ground, it should clean up pretty quickly," Cochrane said. Rescue services at the Waiouru military base, 20 kilometres from the mountain, were placed on full alert. Wives and children of soldiers at Waiouru also were moved to another base yesterday. However, there had been no widespread evacuations, not even the 60 residents of Whakapapa Village on the volcano's slope, where an alarm system would give them 20 minutes warning to run to higher ground if a mud flow heads their way. Institute of Geological and Nuclear Sciences volcanologist Ian Nairn said the volcanic activity is the most sustained since 1945. The Civil Aviation Authority closed the air space over much of the central North Island, concerned that volcanic ash could clog turboprop airplane engines. Two airports -- at Gisborne and Napier -- were closed due to ash falling on the runways. Mount Ruapehu, which is midway between Auckland and the capital Wellington, is the highest volcanic cone on the North Island.