A bizarre video has emerged of a polar bear seemingly trying to eat a baby at St Louis zoo, USA.

The footage, shot on Monday, shows the bear diving close to a baby sitting in front of the enclosure glass.

The bear then catches his breath and dives again with its mouth wide open scaring the baby.

"The polar bear is over 1,200 pounds and was very active, which was highly unusual on a hot Summer day," the filmer wrote online.