Indonesia’s National Disaster Management Agency announced over the weekend that Bali's Mount Agung volcano warning had been raised to a Level Four alert, the highest possible.

Frequent tremors from the volcano have been shaking the area around Mount Agung, and more than 48,000 residents have been evacuated from an exclusion area 7.5 miles around the volcano, according to CNN.

On Thursday, September 21, the U.S. Embassy in Jakarta issued a Bali volcano eruption alert for U.S. citizens in Indonesia.

“Hiking and trekking on the mountain is strictly prohibited,” the statement read. “Hazards from an eruption could include falling ash and, potentially, lava flows. A large eruption and ash emissions could impact air travel in the region.”

The United Kingdom, Australia, New Zealand, and Singapore issued similar travel warnings on Monday.

Should Mount Agung erupt, Ngurah Rai International Airport, in Bali, has a contingency plan in place. Flights will be rerouted to nine regional airports, including Juanda Airport in Surabaya.

Travelers are being urged to reconfirm plans with airlines and tour operators, and to check for Bali volcano updates and news issued by local geological and volcanology agencies.

Mount Agung, which is a popular destination for hikers who scale the 9,944-foot volcano in Bali, last erupted in 1963 — more than 1,000 people died in the disaster.