Searchers will deploy an underwater vehicle as soon as possible to comb sea bed for debris of missing Malaysian flight MH370, the search chief said on Monday.

Australian navy ship "Ocean Shield will cease searching with the towed pinger locator later today and deploy the autonomous underwater vehicle Bluefin-21 as soon as possible," said Angus Houston, who heads the Joint Agency Coordination Center in the multi-national search.

The Bluefin-21 underwater vehicle will initially cover an area of 40 square kilometers. Using its sonar equipments, the mini-sub will send back a high-resolution 3D map of the ocean floor for analysts to sort out possible debris of the missing plane.

The decision to deploy underwater vehicle was announced after no new confirmed signals have been detected since Tuesday, indicating that the batteries of the aircraft black boxes may have died 38 days after MH370 mysteriously disappeared en route from Kuala Lumpur to Beijing,

"It's time to go underwater," Houston said, stressing that the following process would be "slow and painstaking."

As a new encouraging lead, Ocean Shield discovered oil slick on Sunday in the search area where it had heard four signals possibly related to MH370.

But the source of the oil slick remained to be analyzed, Houston said.