Han had led the way at Luxehills International Country Club on day one after an opening 64, but could not sustain the pace during the second round as a 70 saw him slip down the leaderboard.
The 19 year old former Asian Amateur Champion birdied five of his first seven holes and despite only picking up one more shot in the next seven, he avoided any bogeys and was six under for the day with four to play.
That took him to 16 under, alongside big-hitting Colsaerts who is still seeking a maiden European Tour title.
The Belgian used his power to eagle the par five opener, and added three further birdies with just one dropped shot to be four under for his round through ten.
Ireland's Peter Lawrie and South African Keith Horne shared third on 15 under, with both players also through ten holes.
Overnight leader Jamie Donaldson was amongst those one further back as he reached the turn one under for the day, with France's Grégory Havret, Northern Ireland's Gareth Maybin and Dane Søren Kjeldsen alongside him.