Chinese naval vessels on Tuesday expanded the search area in the Indian Ocean for the missing Malaysia Airlines plane in a bid to pick up suspicious pulse signals detected over the weekend.

Amid heavy rain and surging waves, Jinggangshan, an amphibious landing vessel, continued a visual lookout and underwater detection in a new target area of 134 square nautical miles (460 square km), located more than 1,000 km off Australia's western coast.

The Chinese naval vessel has sailed about 18,000 km since it started the search mission on March 9.

Two other Chinese ships, Haixun 01 and Donghaijiu 101, also joined the search operation with Jinggangshan on the suspicious spot of 25 degrees south latitude and 101 degrees east longitude, where Haixun 01 detected a pulse signal consistent with flight recorders on Friday.

On Monday night, the Chinese navy's transport dock Kunlunshan and missile destroyer Haikou steered to another newly-designated area more than 900 nautical miles off Australia's western coast, an area of 11,700 square nautical miles located at about 19 to 22 degrees south and 94 to 97 degrees east.

On Friday, Chinese patrol vessel Haixun 01 detected a pulse signal with a frequency of 37.5 kHz -- the same as those emitted by flight recorders -- in the new search area, and re-detected the pings for 90 seconds on Saturday just 2 km away from the original spot.

However, neither of the signals has been confirmed as related to the missing Boeing 777, said the China Maritime Search and Rescue Center.

Since Flight MH370 disappeared early March 8 with 239 people on board from Kuala Lumpur to Beijing, the Chinese navy has dispatched nine ships to waters in the Gulf of Thailand, near Sumatra Island, and in the southern Indian Ocean, scouring areas of around 340,000 square km.

On Tuesday, an Australian official said no submersible onboard the Australian vessel Ocean Shield would be deployed unless the ship detects more credible signal.

Angus Houston, who heads the Joint Agency Coordination Center (JACC) that oversees an international joint search mission for the missing flight, told reporters that Ocean Shield had failed to receive more transmissions since it detected electronic pulse signals twice two days ago.

He said more detection is important since it can narrow down focus on visual search for wreckage.

"The towed-pinger locator work continues; there have been no further contacts with any transmission and we need to continue for several days right up to the point at which there's absolutely no doubt that the batteries will have expired," Houston said.

He said there would be no deployment of the submersible unless Ocean Shield gets another transmission which "we would have a better idea what's down there and we will go down there to have a look."

"If we go down now and scour the ocean floor, it will be painstaking work."

Meanwhile, Australian Defense Minister David Johnston said his country is "throwing everything on the difficult and complex task" and he predicted several days of intense action ahead of the search team since the lead was positive.

On Saturday and Sunday, the towed-pinger locator deployed from Ocean Shield also detected signals consistent with those emitted from aircraft black boxes at separate locations.

Houston has described the new leads as "very encouraging and promising," saying it might be "the best information" the international search team has now.

According to the JACC, up to 11 military planes, three civil planes and 14 ships assisted in Tuesday's search for MH370. But despite massive multinational efforts, no hard evidence has so far been acquired about the whereabouts of the ill-fated jetliner. Endi