The incident sparked a diplomatic dispute between Singapore and China, which has sovereignty over Hong Kong.
Hong Kong officials said there had been a suspected breach of law and that there could be criminal prosecution.
Singapore had demanded the release of the vehicles, which were being transported by a commercial carrier. It said they were property of a sovereign state so had diplomatic immunity.
`A positive outcome`
The incident put a strain on an already tense relationship between Singapore and China, which controls Hong Kong`s foreign affairs.
Beijing has been angered by what it sees as Singapore`s support for countries which oppose its claims to large areas of contested territory in the South China Sea.
Singapore also has a close relationship with Taiwan and, lacking land space itself, has trained its troops there for decades.
China views Taiwan as a breakaway Chinese province which will one day be reunited with the mainland, by force if necessary.
Hong Kong officials said on Tuesday they had now completed their investigations and the vehicles would be sent back, but that legal action could still be taken.
Singapore`s foreign ministry said it was a "positive outcome" and thanked Hong Kong for its "co-operation in resolving this matter".
In a Facebook post referencing the upcoming Lunar New Year celebrations this weekend, Defence Minister Ng Eng Hen said he was "looking forward to this happy reunion with all Singaporeans in the Year of the Rooster".
More about:
