Bjorn had three birdies on both the front and back nines with a bogey-free round to climb from a tie for sixth place into a share of the lead. He was playing for just the second time in two months.
Overnight leader Hansen bogeyed his last three holes for a 1-under 71 at Gut Larchenhof, falling into a tie with Bjorn at 12-under 204.
The two Danes had a one-shot lead on Alastair Forsyth, who posted nine birdies, an eagle and one bogey for a 62, but was still two shots off the course record. He stood at 11-under 205.
Overall, there were 11 players within five shots of the leaders.