PERTH (AFP) - A mini-submarine making its second dive in the hunt for missing Malaysian jet MH370 encountered a "technical difficulty" and resurfaced on Wednesday, officials said, after the first mission also aborted.

"The Autonomous Underwater Vehicle, Bluefin-21, was forced to resurface this morning to rectify a technical issue," Australia's Joint Agency Coordination Centre (JACC) said. "Bluefin-21 was then redeployed and it is currently continuing its underwater search."

Data was downloaded from the unmanned vehicle while on the deck of the Australian vessel Ocean Shield, which has led the search for the Malaysia Airlines Boeing 777 that vanished on March 8 with 239 people aboard.

"Initial analysis of the data downloaded this morning indicates no significant detections," the JACC said.

The first mission which began on Monday night aborted automatically after breaching the machine's maximum operating depth of 4,500m. Analysis of its sonar data came up with a blank.

The Bluefin was undamaged and embarked on a second sonar sweep of the Indian Ocean seabed from Tuesday night.

The US Navy has estimated it will take the torpedo-shaped vehicle from six weeks to two months to scan the entire search area.

JACC says it would normally spend 16 hours collecting data and four hours diviing down and re-surfacing. The first mission gathered six hours of data.