"They are objects of a reasonable size and probably awash with water moving up and down over the surface," John Young, general manager of the emergency response division of AMSA, told reporters.
Australia has sent four search aircraft and two ships to an area south of the search zone in the southern Indian Ocean it identified earlier this week to search for the objects pinpointed by satellites.
Water in the search area was "several thousand meters deep" and poor visibility in the area would hamper the search, although the weather was moderate, Young said.