* China head Jason Luo resigns, effective immediately
* Luo took Ford China reins in August last year
* Ford falling behind rivals in world's top auto market (Recasts, adds details on Ford sales slump, changes media slug)
BEIJING, Jan 29 (Reuters) - Ford Motor Co said its China chief, Jason Luo, has stepped down after only five months at the helm for personal reasons, a sudden resignation that raises questions over how the automaker will best tackle a sales slump in the world's biggest car market.
Luo had been poached from Key Safety Systems, and it had been hoped that he would reprise his work at the auto parts maker where he engineered a significant surge in China revenue.
He also oversaw its $920 million sale to China's Ningbo Joyson Electronic and the $1.6 billion purchase of assets from bankrupt Japanese airbag maker Takata Corp.
"Jason offered his resignation for personal reasons that predate his time at Ford," Peter Fleet, head of Ford's Asia Pacific operations, said in the statement.
"Ford accepted Jason's resignation as the right way for him and the company to proceed. Jason's decision was not related to the business strategy or performance of Ford China," Fleet said, adding that Luo's replacement would be the subject of a future announcement.
The departure, effective immediately, is a blow to Ford, which has been falling behind rivals in the market. Its China sales slid 6 percent in 2017 compared with a 3 percent rise for the industry overall.
Luo was meant to help the firm improve ties with local joint-venture partners like Chongqing Changan Automobile Co and be nimbler in responding to local consumer demands.
At Ford, Luo was in charge of the carmaker's operations in Greater China including its import business, Lincoln, its passenger car joint venture Changan Ford, its commercial vehicle investment in Jiangling Motors Corporation, and its Taiwan operations.
Foreign automakers in China are also battling fierce competition from local rivals, who are aggressively launching new models to grab market share. The market is also skewed by heavy government support for electric vehicles, prompting Ford and others to seek partners and expand local production. (Reporting by Norihiko Shirouzu; Additional reporting by Adam Jourdan in SHANGHAI; Editing by Jacqueline Wong and Edwina Gibbs)