The State Department on Thursday advised U.S. citizens to avoid all international travel as the world grapples with the Chinese coronavirus pandemic.

“The Department of State advises U.S. citizens to avoid all international travel due to the global impact of COVID-19,” the advisory, the highest of its kind, reads. “In countries where commercial departure options remain available, U.S. citizens who live in the United States should arrange for immediate return to the United States, unless they are prepared to remain abroad for an indefinite period. U.S. citizens who live abroad should avoid all international travel.”

Travel Advisory: Level 4 – The Department of State advises U.S. citizens to avoid all international travel due to the global impact of #COVID19. In countries where commercial departure options remain available, U.S. citizens who live in the US should arrange for immediate return. pic.twitter.com/MydSzFffYd — Travel – State Dept (@TravelGov) March 19, 2020

The development comes after the State Department suspended “routine visa services in most countries worldwide” for both immigrants and nonimmigrants. Countries impacted by the move include, Brazil, the United Kingdom, Germany, China, Israel, South Korea, Italy, Japan, France, India, Denmark, Turkey. “As resources allow, embassies and consulates will continue to provide urgent and emergency visa services. These Embassies will resume routine visa services as soon as possible but are unable to provide a specific date at this time,” the State Department said.

Until the upgrade, the department’s advice to U.S. citizens was to “reconsider” all international travel under what is known as a “level three” alert. The global “level four” warning was unprecedented as such alerts are generally reserved for specific countries embroiled in conflict, natural disasters or where Americans face specific risks.

However, the upgrade will likely have little practical effect because it is not mandatory and there are now limited transportation options for international travel. The only way to ban Americans from going abroad would be to invalidate the use of U.S. passports for such travel, a bar that is currently in place only for North Korea.

The Associated Press contributed to this report.