Boeing (BA - Get Report) shares tumbled Monday but came off sharp lows after China's aviation regulator grounded all Boeing 737 MAX 8 jets operated by its airlines, about 100 aircraft, following a crash of one of the planes that killed all 157 on board.

The Ethiopian Airlines flight - en route to Nairobi, Kenya from Addis Ababa, Ethiopia -- took off Sunday morning and lost contact with air traffic controllers minutes later. It was the second 737 MAX crash since last year. In October, a Lion Air flight crashed in Indonesia.

Ethiopian Airlines said it had grounded its fleet of Boeing 737 MAX 8 jets, while Cayman Airways also said it was doing the same "until more information is received."

The Civil Aviation Administration of China said the order was issued at 9:00 a.m. (0100 GMT) on Monday and would last nine hours.

The agency the order was "taken in line with the management principle of zero tolerance for security risks," because the crash was the second in six months for the 737 MAX 8 jet.

India's air safety regulator said Monday it was reviewing Boeing 737 MAX 8 safety issues after the Ethiopian Airlines crash, Reuters reported.

"Boeing is deeply saddened to learn of the passing of the passengers and crew on Ethiopian Airlines Flight 302, a 737 MAX 8 airplane," the aerospace giant said in a statement. "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 a technical team was headed to the crash site to help the Ethiopia Accident Investigation Bureau and U.S. National Transportation Safety Board.

Southwest Airlines  (LUV - Get Report) said it was "confident in the safety of our fleet" including its 31 737 MAX 8 planes. Southwest is the biggest operator of the MAX 8. Southwest shares fell 1.5%.

Boeing shares fell 6.6% to $394.67 in trading Monday. The stock had declined nearly 13% soon after opening.