A Chinese relative of passengers on the missing Malaysia Airlines flight MH370 waits for the new information at a hotel in Beijing on April 3, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO/WANG ZHAO/GETTY IMAGES. 

Time is running out for searchers to find the black box inside a missing Malaysian airliner.  

Advanced equipment to detect the black box will arrive in the search area in the southern Indian Ocean tomorrow.  

However, until searchers pin down the approximate location of Malaysia Airlines Flight 370, the black box locator will be of little use.

Experts expect the batteries on the jet's black box to run out within a few days.

Australian Prime Minister Tony Abbott calls the hunt for the missing plane "the most difficult search ever undertaken."

Today, he promised to do everything humanly possible to get to the bottom of what's become an international mystery.  

At the same time, friends and family members of the passengers and crew on Malaysia Airlines Flight 370 refuse to give up hope that there could be survivors.  

The Malaysian prime minister is in Australia this week to oversee search and rescue efforts.

The jet took off nearly a month ago from Kuala Lumpur with 239 people on board. It was headed to Beijing but never arrived.  

Meanwhile, a criminal probe is being launched by Malaysian authorities into the flight's disappearance.

One police chief says the investigation still may not reveal what happened to the doomed jet.  

The Malaysian Police Inspector General said all of the passengers on board the flight have been cleared of any role in the plane's disappearance.