COSMODROME—Booster rocket carrying a Soyuz spacecraft with a Russian and US astronaut on board headed for the International Space Station failed in mid-air on Thursday, forcing the crew to make an emergency landing.

U.S. astronaut Nick Hague and Russian cosmonaut Alexei Ovchinin landed safely without any harm.

Russian Deputy Prime Minister Yuri Borisov, quoted by Interfax, said the problem occurred when the first and second stages of the booster rocket were in the process of separating.

The rocket was launched from the Soviet-era cosmodrome in Baikonur, Kazakhstan. A Reuters reporter who observed the launch from around 1 km away said that it had gone smoothly in its initial stage.

“Search and rescue teams are in the air and heading towards the expected touchdown location for the Soyuz spacecraft returning to Earth carrying two crew members,” NASA said in a statement.