"They are improving all the time, (they are) ... making huge investments," said Jim Albaugh, head of Boeing's commercial aircraft operations.
It will "probably be sooner than anyone thinks ... (for them) to make their first competitive sale," Albaugh said, adding that China has made a huge national commitment of money and intellectual resources to the industry.
Replying to a question about a possible competitive threat from China, Albaugh said Boeing had to stay one step ahead of China -- and of other emerging players such as Brazil and Russia.
"Boeing must make sure that we are building tomorrow's plane while they are building today's ... we have to maintain that (technology) edge," he told a briefing ahead of the Paris International Airshow which opens Monday.
"We are assuming that some (of the new players) will be successful ... we are taking them very, very seriously."
China is a hugely important market for Boeing and its European rival Airbus but Beijing has long made clear that it wants to make its own aircraft, to be independent of the foreign majors.
Commercial Aircraft Corp of China (Comac) is making its first appearance at the airshow next week, with a mock-up of the cockpit and part of the fuselage of its C919 model which targets the key medium-haul market dominated by Boeing's B737 and Airbus' A320 series.
Currently under development, the 190-seat C919 is due to enter service in 2016, just after Airbus' upgraded A320neo.
Comac has won orders for some 100 C919s from Chinese airlines but has found only one foreign customer -- the leasing arm of US conglomerate General Electric.
It has technical tie-ups with Canada's Bombardier and CFM International, the Franco-American firm supplying engines for the C919, among others.
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