China has no clear timetable to resume flights of the Boeing 737 Max 8 passenger jet after two fatal crashes of the model, which killed a total of 346 passengers and crew, the civil aviation authority said on Tuesday.

Xu Chaoqun, head of the airworthiness certification department at the Civil Aviation Administration of China, said China will not resume flights of the Boeing 737 Max 8 until the aircraft design meets the country's airworthiness requirements, including any alterations to its control systems.

"The administration will fully review the design, operating principles, configuration and safety of the model in line with the country's airworthiness standards to make sure it meets the requirements for safe operation," Xu said at a news conference.

As for design alterations and corresponding training for crew members, Xu said the administration will ensure that every aircraft is properly modified and that pilots complete training for flight safety.

Xu added that the administration will evaluate the alterations to the jet's design and engine placement, which Boeing had modified for the Max 8 model. Training requirements for pilots will also be evaluated.

The administration has sent two experts to join the US Federal Aviation Administration's panel to review the automated flight control system and airworthiness of Boeing's 737 Max 8 jets, Xu said.

Boeing submitted an application for airworthiness approval of the aircraft to the administration on March 15. The administration is still waiting for a response from the company after raising questions about its flight control system and alterations, Xu said.

China was the first nation to ground all 96 of its Boeing 737 Max 8 jets after two aircraft of that type crashed in the last five months. China also temporarily stopped issuing airworthiness certificates for the jets.

All 157 passengers and crew of a 737 Max 8 operated by Ethiopian Airlines died on Mar 10, including eight Chinese nationals. In October, the same model of plane, operated by Lion Air, went down in the Java Sea, killing 189.