Desperate mission (1965)

A nuclear scientist is kidnapped by Chinese communists in Hong Kong. A Japanese group of judo experts kidnaps him from the kidnappers, but before they can contact the American agent who has been assigned with overseeing the scientist's transfer back to the USA, the agent is killed. The American secret service send their top man to Hong Kong as his replacement, with the mission of locating the scientist. But there are TWO rival gangs of baddies who are also looking for the same target, so our hero has to assume a different identity to infiltrate them.