A Japanese spacecraft showed signs of trouble Saturday after apparently landing on an asteroid and collecting surface samples in an unprecedented mission to bring the extraterrestrial material back to Earth, officials said.

The Hayabusa probe, hovering about three miles from the asteroid, appeared to be shaking, perhaps because of a possible gas leak from a thruster, said Atsushi Akoh, a spokesman for Japan's space agency, JAXA.

JAXA will put Hayabusa into "safety mode" -- which stabilizes the probe by turning its solar panels toward the sun -- for two to three days to investigate, Akoh said.

Communications between the probe and the control center near Tokyo were stable, he said.

JAXA announced earlier Saturday that Hayabusa appeared to have touched down for a few seconds on the asteroid about 180 million miles from Earth, collecting powder from its surface before lifting off again to transmit data to mission controllers.

"The process of sampling also seems to have gone very well," said Kiyotaka Yashiro, another JAXA spokesman.

But the agency will not know for sure whether Hayabusa collected surface samples until it returns to Earth. It is expected to land in Australia's outback in June 2007.

If all goes well, it will be the first time a probe returns to Earth with samples from an asteroid, according to JAXA. A NASA probe collected data for two weeks from the asteroid Eros in 2001, but did not return with samples.