Watch: Moment Nasa astronauts undock from space station
Nasa's SpaceX Crew-11 began its journey back to Earth from the ISS, after a medical emergency prompted the first such return since the orbiting laboratory launched in 1998.
Last week, Nasa announced that a "serious medical condition" with a crew member aboard the ISS led to the decision of bringing the astronaut and three crew members back to Earth months earlier than planned.
Nasa did not identify which of the Crew-11 mission's four astronauts was experiencing the medical issue or describe its nature, citing the crew member's privacy.
The crew includes US astronauts Zena Cardman and Mike Fincke, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Platonov.
