There is an enormous amount of totally “wild” clients arround. Generally I have seen a huge amount of traffic like that (I just copied the first several entries few minutes ago):
ntpdc> mo
remote address port local address count m ver code avgint lstint
===============================================================================
119.147.159.5 8764 161.53.131.133 3825272 3 4 1f0 0 0
106.2.233.43 58085 161.53.131.133 20907303 3 4 1f0 0 0
1.82.184.22 10062 161.53.131.133 10270354 3 4 1f0 0 0
1.82.184.17 34729 161.53.131.133 11434538 3 4 1f0 0 1
36.111.130.57 4360 161.53.131.133 575889 3 4 1f0 7 1
221.181.34.204 54103 161.53.131.133 624369 3 4 1f0 5 1
106.2.233.41 39086 161.53.131.133 9392631 3 4 1f0 0 1
1.82.184.30 2090 161.53.131.133 3991797 3 4 1f0 0 1
124.116.245.14 21884 161.53.131.133 7505310 3 4 1f0 0 1
36.111.130.45 30168 161.53.131.133 934158 3 4 5f0 4 1
14.204.86.98 24602 161.53.131.133 480341 3 4 5f0 6 2
14.204.86.90 16389 161.53.131.133 339827 3 4 5f0 9 2
36.111.130.42 4799 161.53.131.133 373675 3 4 1f0 8 2
119.147.159.6 7009 161.53.131.133 4715482 3 4 1f0 0 2
36.111.130.9 14389 161.53.131.133 551624 3 4 5f0 6 2
111.8.8.230 3054 161.53.131.133 703111 3 4 1f0 4 2
I did make quite an extensive list in ipf when I was trying to battle it, excluding partially even whole subnets, however, I did not take care about it for some time, and there are now, e.g. several IPs with over 10 million requests average 0 seconds, 106.2.233.43 is now on 21 million avg 0 sec.
From relatively recently (second half of 2016 approx.) we (the Internet) have the huge new problem of IoT cameras and many routers from a series of producers having fixed initial root/admin passwords which have to be changed by the end-user. Which they do not, many are probably even not aware of this need. What happend is that there is new virus spread, which tries to log from IP to IP, one after another, searching for any connected equipment with the fixed root/admin passwords. (I see an enormous amount of this ‘telnet’/‘ssh’ trying on my servers, which also sometimes influences the NTP servers availability.) After logging into such a (mostly) internet camera or home router, the Virus can install itself and any other software it likes (because the basis of probably all of that equipment is BusyBox).
Though I have no proof, I have a strong feeling that the enormous, tens of millions of times in a row, amount of NTP requests comes primarily from that equipment (and there are millions of such unprotected IoTs arround!), as I never before last year saw something like that.
The China zone is full of such misbehaving equipment, i tracerouted some of the incoming requests.
Presently my China zone server copes reasonably well (http://www.pool.ntp.org/scores/161.53.131.133), but you can see regular drops at certain times. However, I would not say that I would have any connectivity problems, as the internal network is multiple 100Mb/s and the external connection is 2 * 2 Gbit/s (if not upgraded last several years) (Rudjer Boshkovich Institute, Zagreb, Croatia). This server is a SunFire X4100 (2 * dual AMD Opteron, 2 GHz), Solaris 10. [About what Avij said about “even slower servers” I posted some time ago about my Sun 3/60 (MC68020+68881, 20MHz, 24MiB RAM), SunOS 4.1.1 acting already for years as part of ntp pool, and my web server (http://grgur.irb.hr/) 
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