Authorities sifting through the crash site where Ethiopian Airlines Flight 302 plunged from the sky -- killing all 157 people on board -- said they recovered the aircraft's so-called "black box" Monday, a critical discovery in the search for what caused the disaster.

Ethiopian Airlines announced on Twitter the Digital Flight Data Recorder and Cockpit Voice Recorder had both been recovered from the crash site at Bishoftu, or Debre Zeit, located some 31 miles south of where the plane took off from the capital of Addis Ababa.

An airline official, however, told The Associated Press the box is partially damaged and cautioned: "we will see what we can retrieve from it."

Forensic experts from Israel had arrived to help with the investigation, Ethiopian Airlines' spokesman Asrat Begashaw told reporters. Ethiopian authorities are leading the investigation into the crash with assistance from the U.S., Kenya and others.

"These kinds of things take time," said Kenya's transport minister, James Macharia.

CHINA GROUNDS ALL BOEING 737 MAX 8 PLANES AFTER ETHIOPIAN AIRLINES CRASH KILLS NEARLY 160 PASSENGERS

Red Cross workers were among those who could be seen in photos picking through debris in the crater where the Boeing 737 MAX 8 crashed minutes after takeoff.

Items such as passports, personal documents and shredded books were among the items that littered the field. People from 35 countries, including the U.S., died in the Sunday morning crash, which occurred six minutes after the plane took off from Ethiopia's capital en route to Nairobi. Ethiopian Airlines said the senior pilot issued a distress call and was told to return but all contact was lost shortly afterward.

Even though it's not yet known what caused the new plane to crash in good weather, Ethiopian Airlines announced it decided to ground its remaining four 737 Max 8s until further notice. The disaster had some similarities to the crash of a Lion Air jet of the same Boeing model in Indonesian seas last year, which also occurred minutes after takeoff, killing 189 people.

"Although we don't yet know the cause of the accident, we had to decide to ground the particular fleet as extra safety precaution," the airline said in a statement.

The decision by Ethiopian Airlines to ground its fleet of the aircraft came after earlier announcements by aviation authorities in China and Indonesia to ground the aircraft.

But Andrew Herdman, director general of the Association of Asia Pacific Airlines, told Reuters it was unusual to ground a specific plane type unless a specific issue had been identified and could be inspected.

“In this case it is not clear what the action item is, having done the suspension,” he told the news agency. “What is lacking now is what happened in this case. That means finding the black boxes and piecing together other circumstantial evidence from air traffic control recordings and so on.”

GOVERNMENT OFFICIALS, DOCTORS AMONG ETHIOPIAN CRASH VICTIMS

Other safety experts also cautioned against linking the two air disasters before more is known by investigators.

"I do hope, though, that people will wait for the first results of the investigation instead of jumping to conclusions based on the very little facts that we know so far," Harro Ranter, founder of the Aviation Safety Network, told the Associated Press.

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Boeing said in a statement Sunday a technical team will be traveling to the crash site to provide technical assistance under the direction of the Ethiopia Accident Investigation Bureau and U.S. National Transportation Safety Board.

"We extend our heartfelt sympathies to the families and loved ones of the passengers and crew on board and stand ready to support the Ethiopian Airlines team," the company said.

The Associated Press contributed to this report.