Is chashu Chinese or Japanese?

I'm curious to know, when it comes to the culinary delight known as chashu, does it hail from the rich culinary traditions of China or does it bear the mark of Japanese cuisine? The dish, often featuring thinly sliced, slow-cooked pork belly, is a staple in ramen and other Asian dishes, but its origins seem to be a topic of debate. Could you shed some light on whether chashu is truly a Chinese or Japanese creation, and perhaps provide some insight into its historical and cultural significance?