Too low and too flat to be a tug. No way its a tug without a tall mast for radar and communication radio. There is a tug in front of the ship some distance away and you can compare.
The bottom of the picture is very interesting. You can see a Type 039 Yuan and two Kilos. You can see a Type 022 Houbei, a Jianghu which I wonder why it ain't retired yet, and a Type 072 LST. Sorry make the Yuan a Song.
Let me add there is also a 035 Ming class, another boat that I wonder why its not retired yet, and on the right, could be a semi-submersible? It could be one of those ships that supply to the SCS islands.