You could reasonably ask whether we might be seeing the beginning of a military build-up ready for a re-run of China's 1979 Strafexpedition against Vietnam, which happened in the wake of Vietnam's invasion of Cambodia aimed at toppling the genocidal PRC-backed Khmer Rouge regime, and the enactment of oppressive measures against ethnic Han Chinese in Vietnam. Indeed, the place where the military build-up is reported as occuring (Pingxiang) is exactly the same as where the 1979 invasion was launched from.
All the same, I doubt that conflict will occur. China has little to gain by launching such an invasion. The Sino-Vietnamese land border dispute was settled in 2000. Cambodia (now again a Chinese ally) is not an issue and there is no need to distract the Vietnamese military as there was in 1979. China has nothing to gain through fighting in the South China Seas since they can take whatever they like whenever they like there. Finally the 1979 experience was hardly a positive one for China's military, weakened as it was by the Cultural Revolution that had finished three years previously.
Similarly Vietnam will not gain anything from fighting. The disparity between the armed forces of the two countries has, to say the least, not changed in Vietnam's favour since the 1988 skirmish over Johnston south Reef in which Vietnamese forces were roundly defeated.
Instead this build-up is more likely to be an attempt at sabre-rattling in order to placate the understandable outrage of the Chinese public at what has happened, particularly the nationalists whom the Chinese Communist Party (CCP) counts apon as their main base of support. Indeed, it is hard not to see both sides of this dispute as being the result of what may happen when communist governments, facing the bankruptcy of their ideology, seize on nationalism as a justification for their continued rule. It is easy to see how the violent, government-orchestrated 2005 and 2012 anti-Japanese demonstrations in China could have turned into something resembling last week's anti-Chinese pogrom had the government lost control of them.
In fact we may already be seeing the Chinese government's real response. The Chinese state media is correctly outlining how the violence shows that Vietnam may not be a safe destination for investment, though whether China would stand up to similar analysis based on the same logic is another question. Blame is being placed on the US government, the Chinese government's traditional bug-bear, for their support of Vietnam. All of this speaks of a response based on channeling nationalistic sentiment along paths useful to government, rather than readying them for war - though I would not be surprised to see some 'spontaneous' anti-Vietnam demonstrations in China as well.
[Picture: Vietnamese protesting in Hanoi, 11th of May, 2014. VOA via Wiki]