An Australian ship leading the hunt for missing Malaysian jet MH370 will deploy a mini-sub "as soon as possible", the head of the search said Monday.
"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 fronts the Joint Agency Coordination Centre.
Houston said that in the hunt for the plane's black box transmissions the last signal was logged six days ago.
"We haven't had a single detection in six days so I guess it's time to go underwater," he said at a press conference in Perth.
An oil slick had also been spotted in the search area, Houston said, with around two litres of fuel collected for testing.
"I stress the source of the oil is yet to be determined but the oil slick is approximately 5,500 metres downwind... from the vicinity of the detections picked up by the towed pinger locator on Ocean Shield," he said.
It would be a number of days before the oil could be conclusively tested ashore, but Houston said he did not think it was from a search vessel.
He emphasised that it was 38 days since the Boeing 777 vanished on March 8 and the black box batteries had a shelf life of only 30 days.
The US-made Bluefin-21, a 4.93-metre (16.2 feet) long sonar device will now scour the seabed.
The sonar device, which weighs 750 kilograms, can operate at a depth of up to 4,500 metres -- roughly the depth of the ocean floor where the pings were detected.