"Earlier today, SpaceX conducted a series of engine tests on a Crew Dragon test vehicle on our test stand at Landing Zone 1 in Cape Canaveral, Florida. The initial tests completed successfully but the final test resulted in an anomaly on the test stand.
"Ensuring that our systems meet rigorous safety standards and detecting anomalies like this prior to flight are the main reasons why we test. Our teams are investigating and working closely with our NASA partners."
Officials did not say if this would cause any delay for the launch of a Crew Dragon capsule targeted for July.
SpaceX's Crew Dragon successfully flew without a crew to the International Space Station in March. Officials had previously said the first flight with astronauts could be as early as this summer, but the schedule is under review.