WELLINGTON -- Volcanologists issued a warning on Thursday that Mt. Tongariro in North Island may erupt again any time over the next couple of days or weeks after its blast of ash and steam on Wednesday. According to the Institute of Geological and Nuclear Sciences (GNS Science), Tongariro's activity was 'at a low level' on Thursday although the danger remained high, adding that there is a possibility of an explosion within the next week. Tracking devices revealed that Wednesday's eruption lasted five minutes and the ash column that was ejected reached 3 to 4 kilometers above the Upper Te Maari crater. However, there were no signs of huge blocks spewed far from the crater. GNS Science volcanologist Michael Rosenberg issued a statement saying that they have yet to find proof of magma reaching the surface during the eruption. He explained further that they don't know exactly what Tongariro will do next although based on its previous eruptions, it can be expected that another eruption of the same magnitude may occur any time over the next few weeks. Tongariro's aviation color code was lowered on Thursday from red to orange. Red indicates that an eruption is ongoing with ash being ejected into the atmosphere. On the other hand, orange indicates that an eruption is ongoing although there is little or no ash being spewed. Meanwhile, the Department of Conservation (DOC) stated that the volcanic hazards issued cover an area within a 200-meter radius from the vent. The DOC added that the Tongariro Alpine Crossing remained closed for hikers and trekkers, and its closure will be reviewed on Saturday. ubAlert