Australia vows to continue searching for the missing Malaysian jetliner, as a robotic submarine is about to complete the first phase of its, so far, unsuccessful scan of the Indian Ocean seabed.

The Joint Agency Coordination Center said the Bluefin-21 underwater drone has completed more than 80 percent of its first full mission without finding any "contacts of interest."

Prime Minister Tony Abbott said on Wednesday if the drone fails to locate any debris, authorities will "rethink the search." But, he said, the hunt will not be abandoned. He said the families of the 239 people on board the plane deserve to know what happened.

Defense Minister David Johnston, meanwhile, tells the Associated Press that more powerful, commercial sonar equipment could soon be deployed to help explore the 4.5-kilometer deep search area.

The search effort is currently focused on a 10-kilometer radius surrounding the spot where authorities heard a signal they believe came from the locator beacon on the plane's flight data recorder. The batteries on the so-called "black box" recorder have since run out.

On the ocean surface, ships continue to search a wider area for debris. But for the second consecutive day today, Australian authorities suspended the aerial search because of poor weather conditions.

Malaysian authorities believe someone intentionally diverted the plane as it was heading from Kuala Lumpur to Beijing March 8. But they refuse to rule out the possibility that the Malaysia Airlines jet experienced a major mechanical malfunction