US plane maker Boeing is facing questions after an Ethiopian Airlines 737 crash on Sunday killed all 157 people on board.

It was the second crash in five months involving a 737 Max 8, and comparisons are being drawn with a Lion Air accident in Indonesia last October.

In response, China and Ethiopian Airlines have now grounded all planes of the same model.

However, experts warn it is too early to say what caused the latest disaster.

Ethiopian Airlines says the plane, flight ET302, crashed at 08:44 local time (05:44 GMT), just six minutes after it left Addis Ababa. The aircraft, bound for Nairobi, came down near the town of Bishoftu, 60km (37 miles) south-east of the capital.

The pilot had reported difficulties and had asked to return to Addis Ababa, the airline said.

"At this stage, we cannot rule out anything," Ethiopian Airlines CEO Tewolde Gebremariam told reporters at Bole International Airport in the capital.

Following the Lion Air crash last October, investigators said the pilots had appeared to struggle with an automated system designed to keep the plane from stalling - a new feature of the Boeing 737 Max.

The anti-stall system repeatedly forced the plane's nose down, despite efforts by pilots to correct this, preliminary findings suggest. The crash killed 189 people.

The Lion Air plane was also new and the accident happened soon after take-off.

"It's highly suspicious," Mary Schiavo, former Inspector General of the US Transportation Department, told CNN.

"Here we have a brand-new aircraft that's gone down twice in a year. That rings alarm bells in the aviation industry, because that just doesn't happen."

After last October's crash, Boeing sent an emergency notice to airlines warning them of a problem with the anti-stall system.

However, with the Ethiopian Airlines investigation at an early stage, it is not clear whether the anti-stall system was the cause of Sunday's crash. Aviation experts say other technical issues or human error cannot be discounted.

The investigation will be led by Ethiopian authorities co-ordinating with teams of experts from Boeing and the US National Transportation Safety Board.

An urgent priority for investigators will be to find the plane's two cockpit recorders - one for data and another for pilots' voice recordings. (BBC)

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