How to get the dog out of the kennel when he is scared?

This dog I'm watching is really scared and has severe anxiety. He won't come out of the kennel. It's open. I put a treat next to him and he won't eat it. He's been in it all day and any time I try to pet him he looks really uncomfortable and it seems like he's going to bite me. He won't make eye contact with me. I have to walk him. He's been in the kennel for over 12 hours now during the day. I've been really really nice to him and patient but he won't come out on his own. I'm watching him for 5 and a half days so I hope I can get him to warm up somehow. Advice???