U.S. space agency NASA aborted a planned 6.5-hour spacewalk by two astronauts outside the International Space Station on Tuesday, after one of the spacewalkers reported "a buildup of water" inside his helmet.

"A little more than one hour into Tuesday's spacewalk, Luca Parmitano of the European Space Agency reported water floating behind his head inside his helmet," NASA said in a statement. "The water was not an immediate health hazard for Parmitano, but Mission Control decided to end the spacewalk early."

Chris Cassidy of NASA and Parmitano are already safely back in the space station, and engineers are continuing to evaluate data to determine the cause of the leak, the agency said.

The spacewalk officially ended at 9:29 a.m. EDT (1329 GMT), only 1 hour and 32 minutes into the planned 6.5-hour venture outside the space station, making it the second shortest in the orbital laboratory's history.

Both astronauts had planned to lay wires for the arrival of a new Russian Multipurpose Laboratory Module later this year and to do other maintenance works.

Mission managers will work to identify when the unfinished tasks will be completed, NASA said, adding that none of those tasks are urgent, and that the crew and station are not in any danger.

Source: Xinhuanet