KUALA LUMPUR, Malaysia – More than three weeks after Malaysia Airlines Flight 370 disappeared, and with still no trace of the missing plane, the international search effort intensified Sunday with nine planes and eight naval vessels scouring the latest search area, about 1,100 miles west of Perth, Australia, officials said.

Other ships were en route to the zone and were expected to arrive in the next several days, including an Australian naval vessel, the Ocean Shield, outfitted with special equipment to detect the pings of the plane’s data recorders, or black boxes, according to the Australian Maritime Safety Authority, which is coordinating the search.

As in the two previous days of searching, aircraft spotted more debris floating in the zone’s rough waters, the authority said. On Saturday, crews on two of the ships pulled several objects from the zone’s rough waters, raising hopes that perhaps the first physical evidence of the missing Boeing 777-200 had been found.

But the debris turned out to be “fishing equipment and other flotsam,” the authority said in a statement late Sunday.

In Malaysia, more than two dozen relatives of Chinese passengers on Flight 370 arrived from China on Sunday to press Malaysian officials for more answers about the investigation. The Malaysian government has endured withering criticism by the relatives and friends of Chinese passengers, both in Malaysia and in China, who have accused officials of withholding information about the disappearance of the plane and not doing enough to find it.

The group staged a protest at a hotel near Kuala Lumpur and demanded an apology from the Malaysian government for declaring last week that the plane had crashed into the Indian Ocean, saying there was insufficient evidence to support that conclusion.

Government officials said later that they planned to hold a briefing for the family members that would include “high-level representatives of the Malaysian government.”

The Ocean Shield, an offshore support vessel that will be carrying the ping-detecting listening device, was supposed to depart from Perth on Sunday, but its departure was rescheduled for today, officials said. The ship will also be carrying an unmanned underwater vehicle.

But the ping detector’s utility, in the absence of more-specific information about the location of the wreckage, is questionable.

The device will be towed behind the ship at no more than about 5 knots (about 6 mph) and needs to be within about a mile of the black boxes to pick up the signal reliably, making for a slow and painstaking process. The new search area, which was established Friday, is roughly the size of Poland.

Searchers, however, say there is no time to waste: The device will be ineffective once the batteries powering the black boxes die, which is expected to happen next week.

The recovery of debris from Flight 370 might also help pinpoint the location of the wreckage, though experts are doubtful.

When debris is found quickly enough after a crash into the sea, investigators can trace its drift back to the impact site and conduct an underwater search for the black boxes.

But in the case of Flight 370, any debris, if found, might well have drifted hundreds of miles since the plane’s disappearance and be of limited use in locating the crash site.

Still, recovered items from the plane might allow investigators to rule in or out certain events that could have caused a crash. Scorch marks, for example, might indicate that there was a fire, and the nature of any fire damage could offer clues about its source.