Walls and Ceilings - asbestos shingles

Quick question, I'm trying to install a bathroom vent light, and the outside of my house has asbestos shingles. What is the best way or tool I can use to cut my 4" hole on the shingle so it doesn't brake when I'm cutting it. Any help would be appreciated. Thank you.

Might try placing piece of plywood on spot to be cut with thin screws long enough to go into boards behind siding. Try to place screws so that the holes will be covered by flange on vent when removed and flange put on. If not just putty the holes up when finished with either color matched weather-proof caulk or touch-up paint. Make sure there are no electrical wires or studs in place to be cut and mark the place on the plywood. Drill hole large enough inside marked area to accept saw blade being used. While pushing firmly against plywood to avoid excess vibration on the siding, use a medium to fine toothed saws-all or jig saw and slowly cut from hole to mark and follow line. Be especially careful when cutting into the overlap of siding of it overlaps. Do not start saw until firmly against wall and do not remove saw from siding until blade has completely stopped. By keeping firm pressure on saw against siding (enough to keep siding or saw from bouncing) and taking your time, you should be able to cut it with no problem.

P.S. When doing something like this, I usually mark spot to be cut from inside and drill a small (level)hole in the center to outside or just to where the bit starts to come through to leave a center mark. Then make mark on outside using my hole as center guide. Hope this helps. Have a good day.