I recommend you hit the three switches that are in the northern end of the corridor you went though, as unlocking the door has a prize, and more importantly, a save point.
To the south of the door, to answer your question, are two guards. The corridor is about 4 spaces long, with two guards off the screen. One guard is stationary in the leftmost space, and he alternates between looking to the east and to the south. To his right is the other guard, who strafes back and forth between the 3 remaining spaces. He constantly looks to the north. Getting past these guards will require precise timing, as there is no room for error.