(CNN) -- The Chinese may be further along in developing a radar-evading fighter jet than U.S. intelligence has thought, the U.S. defense secretary said.
Images and cellphone video of the stealth fighter, known as the J-20, conducting tests on a runway surfaced recently on the internet.
Defense Secretary Robert Gates spoke to reporters Saturday, as he prepared to leave for Beijing in an effort to create better and more open relations with the Chinese military.
"I think that what we've seen is that they may be somewhat further ahead in the development of that aircraft than our intelligence had earlier predicted," Gates said in answer to a question.
Gates has said previously that the Chinese aircraft would not be fully operational until 2020 or 2025 and that even then the U.S. would have thousands of similar aircraft compared to just a "handful" produced by the Chinese.
Analysts believe the J-20 stealth fighter will have the radar-evading capability of fifth-generation fighters produced by the United States, such as the F-22 and F-35. But Gates questioned how advanced that capability will be.
"I think there is some question about just how stealthy," Gates said.
The defense secretary also said he is still concerned about Chinese progress in developing an anti-ship cruise and ballistic missile which could potentially target U.S. vessels in the region.
"They clearly have the potential to put some of our capabilities at risk, and we have to pay attention to them, we have to respond appropriately with our own programs," Gates said. "My hope is that through the strategic dialogue that I'm talking about that maybe the need for some of these capabilities is reduced."