Jakarta, Indonesia (CNN) -- Indonesia's Mount Merapi erupted again Saturday, spewing hot ash clouds for more than 20 minutes followed by lava and sending nearly residents fleeing in panic for the second time in a week.
The volcano's rumblings were felt within a radius of 12 kilometers (7 miles), said Surono, head of the Indonesia Volcanology and Geological Disaster Mitigation Agency, in a report posted on the agency's website. Like many Indonesians, Surono uses only one name.
As the second eruption occurred shortly after midnight local time (1 p.m. Friday ET), thousands of evacuees already living in temporary shelters were moved farther away from the mountain.
"I was so scared," said Natya, 48. "I heard this loud sound from the volcano. We were told to get on a police truck. I was panicking."
Ash clouds reached the main city of Yogyakarta, about 30 kilometers (18 miles) away, the agency said. The ash covered the city of 400,000 like a film, limiting visibility to about 10 to 15 meters (32 to 49 feet). People in the city wore masks or held handkerchiefs to their faces. The ash disrupted air traffic at Yogyakarta's Adisucipto Airport, delaying inbound and outbound planes.
Mount Merapi began erupting Tuesday. It appeared to calm following the eruption early Saturday, but authorities said the alert level remained at its highest.
On Friday, a major blast from Merapi spewed hot ash clouds and lava in the sky and sent people into the streets. It was one of at least six eruptions Friday, which prompted officials to warn residents to be on high alert and stay away from the volcano. One eruption on Friday sent a massive plume about 1,500 meters (4,921 feet) high above the mountaintop, according to extreme weather chaser James Reynolds. Ash drifted to the south after the eruption, he said.
Residents started streaming down the mountain, heading for safer ground, as the eruptions took place Friday. Some were being evacuated after returning home following eruptions earlier in the week, the volcanology agency said.
Those living within a radius of 10 kilometers (6.2 miles) of Merapi may have to be relocated, said a police official in Yogyakarta.
Thirty-eight people died in the eruption or from injuries, officials said.
Officials fear more eruptions, the head of the country's volcanology agency said Saturday, according to the Antara news agency.
Chief Inspector Gen. Ondang Sutasna told local television that he toured the area and believes that some places will be too dangerous to allow rebuilding.
Rescue and recovery efforts continue to unfold, with the Indonesian government scrambling to help tens of thousands of residents displaced by the eruption.
Mount Merapi, which looms on the horizon north of Yogyakarta, is one of Indonesia's most active volcanoes and lies in one of the world's most densely populated areas. The volcano has a summit elevation of nearly 10,000 feet (3,000 meters).
CNN's Kathy Quiano contributed to this report.