One of Russia’s most active volcanoes has erupted, sending a five-kilometer-high cloud of ash into the sky over the eastern Kamchatka Peninsula. A “Code Red” warning was briefly issued for aircraft.

The Academy’s Institute of Volcanology and Seismology released a video showing the ash cloud over Shiveluch, which stretched for more than 490 km east and southeast of the volcano.

The Ebeko volcano on the Kuril Islands also emitted ash 2.5 kilometers high, the institute said. It was not explicitly stated whether the eruptions were triggered by the earthquake.

A red-category ash cloud warning briefly put all aircraft in the region on alert, the Kamchatka Volcanic Eruption Response Team reported. A separate report by the official Tass news agency said on Sunday that no commercial flights had been disrupted and no damage had been caused to aviation infrastructure.

The tremors in the region could be a harbinger of an even stronger earthquake in southeastern Kamchatka, Russian scientists warned. The Institute of Volcanology and Seismology said a possible second earthquake could occur “within 24 hours” with a magnitude of nearly 9.0.

Russian news agencies reported the strongest earthquakes “in a long time,” citing residents of Petropavlovsk-Kamchatsky, a port city of more than 181,000 people located across from a bay with a major Russian submarine base.

On November 4, 1952, a magnitude 9.0 earthquake caused damage in Kamchatka but no fatalities, although it triggered 9.1-meter-high waves in Hawaii.