Moore, 61, has cancelled all his upcoming work commitments, and is hoping to be discharged before the weekend so that he can continue his recovery at home.
"I'm writing this to all of you... From the Intensive Care Unit at a hospital in New York City," he writes in a message posted on Facebook.
"Unfortunately, I've come down with pneumonia. Between running all over the place lately promoting my new movie... plus going to Flint to help the people of my hometown (deal with a dirty water crisis)... You can't burn it at both ends, and if u (you) do, it's best not to do so in the winter nor anywhere near a place full of toxic water!