A volcano approximately 600 km southeast of the Philippine capital spewed ash before dawn on Sunday, a week after a phreatic eruption that prompted authorities to raise the alert level to 1 and evacuate residents to safety. The Philippine Institute of Volcanology and Seismology said it detected a phreatic explosion again in Bulusan volcano in Sorsogon province at 3:37 a.m. local time on Sunday. "The event lasted 18 minutes based on the seismic record, but the eruption plume was not visible in camera monitors," the institute said. On June 5, authorities evacuated more than 200 residents near the volcano after spilling a grey plume about a kilometer high into the sky. The "phreatic eruption" lasted approximately 17 minutes and ashfall was reported in towns near the volcano. READ: First aid flights leave for Tonga after big volcano eruption The volcano remains on alert level 1 on a scale of 5, meaning that the volcano is still in an "abnormal condition." The institute urged people to stay away from the four-kilometer "permanent danger zone." The institute also advised pilots to avoid flying close to the volcano's summit as ash from any sudden phreatic eruption can be hazardous to aircraft. Bulusan volcano is one of the Philippines' most active volcanoes. In January 2018, the volcano spewed ash about 2.5 km high into the sky.