Police are still searching for a Chinese couple whose car is believed to have gone off a cliff in California after they were visiting parks in the state.

The Chinese Consulate General in San Francisco is working with authorities, including the California Highway Patrol and the Fresno County Sheriff's Office, to find the couple, Jie Song, 30, and her husband, Yinan Wang, 31, who were reported missing on Aug 11.

Their car is believed to have gone off a cliff and into the Kings River off Highway 180, where part of the vehicle was located on Aug 14 by the sheriff's office.

According to several of their relatives in the US, the couple were last seen at the Crystal Caves in Sequoia National Park on Aug 6.

They were driving a 2012 white Ford Focus, with license plate number 6XMM431, as they went sightseeing at several known scenic spots in California.

They had planned to stay in a Fresno hotel on Aug 7 before heading to Yosemite National Park the next day. The couple were supposed to return to San Diego on Aug 9, but never arrived.

Law enforcement agencies got a clue days earlier from a sheriff's deputy who saw a California license plate in the brush from a video clip. The plate was the same as the one on the couple's Ford Focus.

The Fresno Bee reported that Tony Botti, a spokesman for the Fresno County Sheriff's Office, said the car was mostly submerged in white-water rapids, so officers haven't been able to determine if the vehicle is intact or bodies are inside.

Botti said they're not ruling out the couple's possible escape, but said it wasn't likely.

Song lives in China for the majority of her time and teaches English at a private school in Hangzhou, Zhejiang province. She has been visiting her husband several times a year since he became a postdoctoral scholar last year at the University of California-San Diego.

Consul Huo Huijian of the consulate's protection department said "we didn't rule out the possibility that they are still alive".

Meanwhile, family members of the couple in China are being offered assistance to streamline application procedures so they can come to the US.

"We didn't want to spread speculation about the couple's situation," said Huo, adding that the consulate general hasn't received any confirmation of the couple's death.

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