Entrance to pilot tunnel for the Aberdeen Tunnel [????- ]

During May's visit to Hong Kong Cemetery, Patricia pointed out this, which looks like a tunnel entrance:

It is set into a hillside at the southern end of the cemetery. If you walk up the slope, you'll see that just behind here is the Aberdeen road tunnel - you can see it clearly if you zoom into the satellite image.

So, if there used to be a tunnel leading back from behind this pink door, it was likely blocked off during construction of the Aberdeen tunnel.

Here's a closer view of the entrance:

There's a wooden door over the gate, then a rusty iron gate behind that, then behind that it seems to have been blocked up with concrete.

So, if we assume it's a tunnel, what type of tunnel is it?

The entrance doesn't look like other Air Raid Precaution tunnels on Hong Kong island. Though the shape, and the iron gate do look a bit like this ARP tunnel below Kowloon Park.

I haven't seen any record of an ARP tunnel in this area though. And I don't think the residents of the cemetery would have been bothered by air raids!

So could it be a Japanese tunnel? So far the Japanese tunnels we've seen have been smaller than this, and not so well finished. It doesn't seem likely.

Does anyone know the story behind this?