PERTH, Australia - A robotic submarine looking for the missing Malaysia Airlines jet is expected to finish searching a patch of the Indian Ocean seabed within a week after so far coming up empty, and the search area may be expanded after that, officials said Saturday.

As the hunt for Flight 370 hit the six-week mark, the Bluefin 21 unmanned sub began its seventh trip into the depths off the coast of western Australia. Its search area forms a 6.2-mile circle around the location of an underwater signal believed to have come from the aircraft's black boxes before their batteries died. The sonar scan of the sea floor in that area is expected to be completed in five to seven days, the search center said in an e-mail to the Associated Press.

The U.S. Navy sub has covered around 51 square miles since Monday. The latest data are being analyzed, but nothing has yet been identified.

Malaysian Defense Minister Hishammuddin Hussein told reporters in Kuala Lumpur that the weekend search was crucial.

"The narrowing of the search for today and tomorrow is at a very critical juncture, so I appeal to everybody around the world to pray and pray hard that we find something to work on over the next couple of days," he said.

He said there were no plans to give up once the Bluefin concludes its work. Rather, he said, the search may be broadened or other tools may be used.

"The search will always continue," he said. "It is just a matter of approach. All efforts will be intensified for the next few days with regards to the underwater search."

Meanwhile on Saturday, up to 11 aircraft and 12 ships continued to scan the ocean surface for debris from the Boeing 777 that disappeared March 8 en route from Kuala Lumpur to Beijing with 239 people on board.

Radar and satellite data show the plane veered far off course for unknown reasons and would have run out of fuel in the remote section of the southern Indian Ocean where the search has been focused. No debris has been recovered since the hunt began.