At some point I found that 手を貸す both literally and figuratively means 'to lend a hand' - is the resemblance a coincidence?
There are a lot of metaphors in common around the world. This is a good example of one such metaphor - the extension is quite logical (give help > give a hand (to help) > lend a hand), and it wouldn't surprise me to find many more examples of similar metaphors around the world.
There are others that are less common, such as Japanese's 猫をかぶる - the idea of 'cat' isn't cross-culturally connected with 'niceness', so the metaphor is relatively unique. (Compare English 'a wolf in sheep's clothing' for the same idea.)
A good place to start reading about these, if you're interested, is Lakoff and Johnson's famous Metaphors We Live By, a good introduction to the roles and mechanics of metaphors in language and culture.