Nasa is shutting down two of its space centres to help prevent the spread of the coronavirus.
The US space agency said it will suspend work at its Michoud facility in New Orleans, where a Moon rocket, or Space Launch System, is being built.
Its Stennis Space Center in Mississippi, where the rocket booster is being tested, will also temporarily close.
This could delay Nasa's mission to send astronauts to the Moon in 2024.
The US now has more than 11,000 confirmed coronavirus cases, including one known case at NASA's Stennis Space Center.
"Nasa will temporarily suspend production and testing of Space Launch System and Orion hardware," said its administrator Jim Bridenstine. The only workers allowed onsite will be those dealing with security and critical infrastructure.
"We realise there will be impacts to Nasa missions, but as our teams work to analyse the full picture and reduce risks we understand that our top priority is the health and safety of the Nasa workforce," Mr Bridenstine added. "There is no team better prepared for doing hard things."
The delays will affect manufacturing and testing of the Space Launch System and Orion, the crew capsule that will carry the astronauts to the Moon. NASA had set a goal of the next Moon landing to happen by the end of 2024.
A test flight without any astronauts aboard, may also be delayed until after 2021.
Another Nasa site, the Kennedy Space Center in Florida, is currently operational. This is the home of its Perserverance rover which is scheduled to head to Mars this summer to look for signs of ancient life and collect rock and soil samples.