Chinese naval vessels have fired on Vietnamese fishing boats a few times ...
Actually it's far worse than that, Vietnamese have been killed on both fishing and government/military boats both around the Spratly/Paracells and in the northern part of Ha Long Bay.
The Chinese are a*reholes of the worst type.
Th Vietnamese Navy has 'tours' out there for people interested in seeing a few hardy souls, tending their gardens and fishing. They also have a weather station and the public power runs from 06.00-22.00H daily.
There is not too much love lost between VN and China, although the really Old Farts in Ha Noi make trips to BeiJing every 5 years.
VN has documentary and archaeological proof they were out there hundreds of years ago which, naturally, China rejects having proclaimed the whole of the South China Sea to be their territory.
Last time VietNam and China fought, in 1979, the Chinese invaded northern VN and lost 20,000 soldiers in 17 days. The Vietnamese loaded the dead in freight cars and pushed them north. During the Chinese withdrawal they blew up every significant bit of infrastructure including bridges and larger buildings. The Russians then befriended VN and the result was some of the ugliest buildings and bridges, etc. you have ever seen.