What is this mysterious dark ring in the sky above Sentosa?

People visiting Sentosa on Sunday afternoon (May 14) were fascinated by a dark ring that appeared in the sky above the recreational island.

A video of the mysterious ring was reposted on SGAG's Facebook page with the caption:

"Is someone doing some SERIOUS VAPING in Sentosa or what? What is this WEIRD RING in the sky??"

Some netizens were quick to jump to an 'alien' explanation while others thought that it might be a bird or insect formation.

Others were convinced that there was a rational explanation to the ring.

They believed that it could be a smoke ring from the fireworks machines used for the Wings of Time show.

What do you think?