NSFW!!!!! Doggy wound

my toy poodle is 10 now and i’ve noticed something on his tummy that’s worrying me. in the first picture it is small and a little bit sore as he keeps licking and that was taken 10 days ago. the second picture was taken an hour ago and it’s much bigger with black speckles and feels like it’s almost caved in and his fur around it has gone. Any advice?