By Stella Qiu and Josh Horwitz
BEIJING/SHANGHAI (Reuters) - China's aviation regulator on Monday grounded nearly 100 Boeing Co 737 MAX 8 aircraft operated by its airlines, more than a quarter of the global fleet of the jets, after a deadly crash of one of the planes in Ethiopia.
However, a U.S. official said it was unclear what information the Chinese regulator was acting on because the investigation of Sunday's crash, the second involving the latest version of the narrowbody jet, was in the early stages.
Speaking on condition of anonymity as the topic is sensitive, the U.S. official said there were no plans to follow suit, as the jet had a stellar safety record in the United States and there was a lack of information on what caused the Ethiopian crash.
Boeing, whose shares dropped 9 percent in U.S. pre-market trade, said the investigation remained in its early stages and it had no basis to issue new guidance to operators.
It was unusual to ground a plane type unless a specific mechanical issue or component failure had been identified and could be inspected, said Andrew Herdman, director general of the Association of Asia Pacific Airlines.
"In this case it is not clear what the action item is, having done the suspension," he said. "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."
Most other Boeing 737 MAX operators globally told Reuters their planes would keep flying and they had no plans to cancel orders.
Sunday's crash, minutes after take-off, of an Ethiopian Airlines 737 MAX 8 bound for Nairobi, killed all 157 on board and prompted the carrier to ground the rest of its 737 MAX jets.
In October, a 737 MAX 8 operated by Indonesian budget carrier Lion Air crashed 13 minutes after take-off from the Indonesian capital of Jakarta on a domestic flight, killing all 189 on board. The 737 MAX 8 first entered service in 2017.
The Civil Aviation Administration of China (CAAC) said it would notify airlines when they could resume flying the jets, after contacting Boeing and the U.S. Federal Aviation Administration (FAA) to ensure flight safety.
"Given that two accidents both involved newly delivered Boeing 737-8 planes and happened during take-off phase, they have some degree of similarity," the CAAC said, adding the step was in line with its principle of zero tolerance of safety hazards. The 737 MAX 8 is sometimes referred to as the 737-8.
The grounding was due to safety concerns and not related to trade friction between the United States and China, Li Jian, the deputy head of the Chinese regulator, told reporters, the Yangcheng Evening News said.
"These are two separate issues," the newspaper, which is backed by the government of the southern province of Guangdong, quoted Li as saying on the sidelines of a parliament meeting in Beijing.
Chinese airlines have 96 737 MAX 8 jets in service, the state company regulator said on Twitter-like Weibo, including Air China, China Eastern Airlines, China Southern Airlines and Hainan Airlines.
Chinese aviation data firm Variflight said at least 29 international and domestic flights on Monday had been cancelled and that airlines had swapped out the plane on 256 other flights that had been scheduled to use it.
China Eastern's chairman, Liu Shaoyong, told financial publication Caixin on the sidelines of the Bejing meeting that it would only consider resuming 737 MAX 8 flights once Boeing issued a safety commitment for the jets and proved there was no aircraft design link between the two crashes.
The cause of the Indonesian crash is still being investigated.
A November preliminary report, before the retrieval of the cockpit voice recorder, focused on airline maintenance and training and the response of a Boeing anti-stall system to a recently replaced sensor but gave no reason for the crash.
Ethiopian Airlines said it had grounded its 737 MAX 8 fleet until further notice as an "extra safety precaution" even though it did not know the cause of Sunday's crash.
The airline has a remaining fleet of four of the aircraft, flight tracking website FlightRadar24 says.
Cayman Airways said it had grounded both of its new 737 MAX 8 jets until it got more information.
But no other airlines with 737 MAX 8s in their fleets or on order, or their regulators, told Reuters they were grounding the aircraft or cancelling orders.
By January-end, Boeing had delivered 350 of the 737 MAX family jets to customers, with 4,661 more on order.
Western industry sources say China has been at pains in recent years to assert its independence as a safety regulator as it negotiates mutual safety standard recognition with regulators in the United States and Europe.
In 2017, it signed a mutual recognition deal with the FAA, but industry sources say it has struggled to gain approval from the FAA that would allow it to sell its self-developed C919 airliner to Western airlines.
The grounding was "reasonable and justified", said Chinese aviation expert Li Xiaojin but added that he did not anticipate a major problem, as Chinese airlines operated fewer than 100 of the aircraft, among a combined fleet of more than 2,000 planes.
(Reporting by Josh Horwitz and John Ruwitch; Additional reporting by Brenda Goh in Shanghai, Stella Qiu in Beijing, David Shepardson in Washington, Tom Westbrook in Sydney, Jamie Freed in Singapore, Cindy Silviana and Edward Davies in Jakarta, Heekyong Yang in Seoul, Tracy Rucinski in Chicago, Alexander Cornwell in Dubai and Tim Hepher in Paris; Writing by Brenda Goh and Jamie Freed; Editing by Robert Birsel and Clarence Fernandez)