The eruption of Anak Krakatau has been confirmed.
One of Volcano Discovery readers spent a night on February 20, 2017, at Anak Krakatau and saw intense strombolian-vulcanian type activity from the summit.

First sign of volcanic activity of Anak Krakatau (Child of Krakatau) were observed via satellite imagery on February 17, 2017, where a strong thermal anomaly was discovered over the summit of the active volcanic peak.

Was Anak Krakatau entering a new eruptive phase?
Eruption confirmed
The new suspected eruption was confirmed on February 20, 2017 by one of the reader of Volcano Discovery who says: ‘I spent last night on the Anak Krakatau and I just saw your post on a new activity, I can confirm that there was a lot of activity yesterday afternoon / night.‘

The above picture, supposed to have been taken on February 17th by Anugera Simanjuntak, shows a very clear plume rising from Krakatau’s crater.

A strong degassing plume is present. Recent eruptive materials have also been found on the flanks of the colossus, probably from the explosions of 17-18.
And the eruption could look like this:
Seismic activity
PVMBG reported that seismicity at Anak Krakatau increased on 17 February. The first earthquakes indicating emissions were followed by continuous tremor. Harmonic tremor were first recorded February 19 at 18:10. Strombolian explosions ejected incandescent material 200 m high at 19:04.