There were no sightings reported by search aircraft or objects recovered by ships on Thursday, the Joint Agency Coordination Centre said.
Friday's search area was about 18,000 square miles (46,700 square kilometers), centered 1,436 miles (2,312 kilometers) northwest of Perth.
That's far smaller than the search area's size a few weeks ago.
"It's pretty incredible, if you look at where we started, which was virtually the entire Indian Ocean, now getting it down to what's essentially a couple hundred square miles (where the pings have been detected) is pretty miraculous," Marks said.
The Ocean Shield first picked up two sets of underwater pulses on Saturday that were of a frequency close to that used by the locator beacons. It heard nothing more until Tuesday, when it reacquired the signals twice. The four signals were within 17 miles of one another.