By Fang Yan and Ken Wills

BEIJING | Wed Sep 7, 2011 10:27pm IST

BEIJING (Reuters) - China will need 5,000 commercial aircraft worth $600 billion over the next 20 years, a senior Boeing executive forecast on Wednesday, a 25 percent increase on the company's previous estimate.

A significant portion of that demand will be small and intermediate-sized jets, Randy Tinseth, vice president of marketing for Boeing Commercial Airplanes, told reporters in Beijing.

Last November, Tinseth estimated China would need 4,330 new planes worth $480 billion, effectively tripling its fleet size over the next 20 years.

Boeing is betting that new Chinese wealth and government spending on infrastructure will bolster travel in the country, where the domestic passenger traffic is growing rapidly.

Tinseth has said the U.S. aircraft maker expects to maintain its market share in China.

Boeing competes with Airbus for commercial plane orders, and Tinseth said that overall Boeing would deliver 485 to 495 airplanes this year, including 25-30 787s Dreamliners and 747-8s.

A spokesman for Airbus declined to comment on the company forecasts for China, but said the country was one of the world's fastest growing markets.

"In 2010 we have delivered every fifth aircraft of our production to China," he said.

Airbus, which currently has a market share of 45 percent in China, is due to publish its global forecasts on Sept. 20.

Largely because of snags in the complex global supply chain, Boeing is about three years behind schedule in delivering the lightweight, carbon-composite 787, which promises hefty fuel savings to airlines.

When asked about the delays, Tinseth said: "We have a plan. We are meeting that plan, and we are committed to that plan. Are there risks? There are always risks. I believe we have turned a corner in terms of production and in terms of design of the airplane."

All Nippon Airways will be the first to take delivery of the 787 on Sept. 25 and expects to have 20 Dreamliners by March 2013.

ANA President Shinichiro Ito told Reuters on Wednesday that ANA expected to receive all 55 Dreamliner jets it has ordered by March 2018.

"We were in big trouble because we had to push back our business plans (due to delays with the Dreamliner)," Ito said in an interview with Reuters in Japan. "I'm so excited to finally be receiving it."

State-backed Commercial Aircraft Corporation of China (COMAC) is developing its own commercial jet C919, which Beijing hopes can eventually compete with Boeing and Airbus.

COMAC said it expected the C919 to have its first test flight in 2014, with deliveries to customers starting in 2016.

At the Paris airshow in June, Ryanair, which currently flies only Boeing jets, signed a deal with COMAC to help it design a rival to Boeing's 737.

Ryanair CEO Michael O'Leary said he expected Chinese manufacturers to take a significant bite of the global market for short-haul planes by 2016.

(Additional reporting by Mariko Katsumura in Tokyo and Elena Berton in Paris; Editing by Will Waterman)