Two volcanoes erupted Thursday on Russia's far-eastern Kamchatka Peninsula, tossing massive ash clouds miles (kilometers) into the air, forcing flights to divert and blanketing one town with thick, heavy ash.

The Klyuchevskaya Sopka, Eurasia's highest active volcano, exploded along with the Shiveluch volcano, 45 miles (70 kilometers) to the northeast, the Russian Emergency Situations Ministry's branch in Kamchatka said, adding that flights in the area had to change course.

Ash clouds from the remote volcanoes billowed up to 33,000 feet (10 kilometers) and were spreading east across the Pacific Ocean, vulcanologist Sergei Senyukov told Rossiya 24 television. Streams of lava flowed down the slopes of Shiveluch.

The U.S. Federal Aviation Administration on Thursday issued a notice to pilots that they should remain alert for possible ash clouds, saying emissions have "intermittently complicated air travel" in the area of the Kamchatkan Peninsula.

"Any air carriers, including foreign air carriers, that observe or experience any difficulties resulting from an encounter with volcanic ash, please notify air traffic control immediately," the notice said.

Several pilots have reported seeing ash clouds in the Alaskan region, FAA spokeswoman Laura Brown said. However, the ash has been below 25,000 feet, while planes are assigned altitudes above that level so there was no difficulty, she said. Thus far FAA hasn't issued any flight restrictions due to ash, she said.

The FAA spokeswoman Tammy Jones said the agency does not anticipate any impact from the eruptions on air traffic to the United States.

The Volcanic Ash Advisory Center in Tokyo issued an advisory for planes to be alert for the ash cloud, although Tokyo's Narita airport said it had no flights diverted yet.

South Korean flights in the region reported no disruptions, according to South Korea's Incheon International Airport Corporation, and South Korea's two main airlines, Korean Air and Asiana Airlines.

Volcanic ash blanketed the nearby town of Ust-Kamchatsk, reducing visibility to only a few feet (meters) and turning buildings ghostly white. Emergency officials said the town's 5,000 residents weren't in any immediate danger but urged them to stay indoors and tightly close doors and windows to avoid inhaling ash particles that could lead to respiratory illnesses and allergic reactions.

Schools and businesses in Ust-Kamchatsk quickly closed and all streets were shut down to traffic. Scientists warned that ashes will likely continue falling on the area for at least 10 days.

Ust-Kamchatsk is 45 miles (70 kilometers) east of Shiveluch and 75 miles (120 kilometers) northeast of Klyuchevskaya Sopka, and winds blew ash from both on the town.

Shiveluch quieted down later Thursday, but Klyuchevskaya Sopka, which stands 15,584 feet (4,750 meters) high, kept erupting, Russian officials said.

Jen Burke, a meteorologist with the Alaska Aviation Weather Unit, said ash from the Shiveluch eruption — the larger of the two — was moving across the Bering Sea at a height of 25,000 feet (7,620 meters). That could put it in the path of planes flying between Asia and North America over Alaska.

"Right now it's not a difficult area to avoid because it's north of the Aleutian Islands," Burke said. "Planes could fly south of the Aleutian Islands and be perfectly safe."

She said ash might affect the extreme west coast of Alaska but winds were predicted to push the cloud north.

Kamchatka, which juts into the Pacific, is studded with active volcanoes.

The Emergency Situations Ministry warned Thursday that another volcano across the peninsula to the south, Gorely, has begun spewing gases and could erupt any moment. Gorely is located about 45 miles (70 kilometers) south of Kamchatka's regional capital, Petropavlovsk-Kamchatsky.

Kamchatka volcanoes are part of the "Ring of Fire" string of volcanoes encircling the Pacific.

The Russian eruptions are not related to the recent activity of Indonesian volcanoes, said Lee Siebert, director of the Smithsonian Institution's Global Volcanism Program. On Tuesday, eruption of the Mount Merapi volcano in Indonesia killed 33 people.