Lots of debunking on this one, the most credible (for me, anyway) stories saying the tanks were on the streets (of just *one* location in *one* city, to judge by the photos, by the way) in preparation for a military parade as part of the 1 August Armed Forces Day celebrations. The presence of crowds of curious civilians, also shown in the photos, taking pictures with their cell phones lends credence to this view. If this were not a drill, the tankers would have enforced a security perimeter far more aggressively, and as John Z says above, we would have heard more about it. TL;DR: Not worthy of genuine concern. We (and Xi ;-) ) have a lot more real issues to be concerned about !