Xiao Li, wife of Chinese sailor Guo Chuan, has called for worldwide rescue efforts to help search for her missing husband.

Guo is thought to have fallen off from his boat on Wednesday, Beijing time, during his trans-Pacific voyage. The US Coast Guard found Guo's boat in the sea off Honolulu, Hawaii on Thursday, but not him.

"The sea temperature is 25 degrees Celsius above and we will not give up till the last hope," she said in a letter shared and forwarded extensively on Chinese social media platforms such as WeChat, QQ and Weibo on Friday afternoon.

The Information Office of Qingdao Municipal Government has confirmed the veracity of the letter. Qingdao, East China's Shandong province, is Guo's hometown. The sailing boat by Guo this time was called Qingdao, China.

"The US side is continuing the search and has expanded the rescue area to 400 nautical miles. Our support team, relatives and friends are contacting more local professional organizations to join in," Xiao said.

"If anyone can provide any contact information of rescue forces from San Francisco, please call me at +86 13901391466."

On its official WeChat platform and website, Guo Chuan's support team made an announcement that they do not prepare to give up search for Guo Chuan.

They are looking for ships having a platform to land aircraft and charge fuel near Hawaii.

"If you have any information about that, please send email to jessie.zhou@chinasportbusiness.com. Thanks a lot for your kindness in advance," the announcement said.

Guo, a professional sailor, was reported to be in good health and confident about the voyage. He already holds two world records for sailing - a solo nonstop circumnavigation world record set in 2013 and an Arctic Ocean Northeast Passage nonstop sailing world record set in 2015.

Guo set sail on his trimaran Qingdao China from San Francisco's iconic Golden Gate Bridge on Oct 18 for Shanghai hoping to set a new world record for solo crossing.