You can say "There seems to be ___" when you notice something but you're not completely sure that you have identified it correctly. For example, if you are on a city street and notice that there are tons of people all walking toward somewhere, and many of them are wearing green shirts, you can say:
There seems to be a parade going on.
You say "there seems to be a parade" because you're not sure that it's really a parade. There might be some other event happening, like a concert or a baseball game, instead.