Heart-stopping video has emerged of a naïve swimmer frantically trying to reach the shore as a large crocodile takes chase in Mexico.

The amateur footage shows the adrenalin-charged young male making a beeline for dry land, as panicked tourists on the overhanging Boca Paila bridge in Sian Ka'an watch on in terror.

Just as the metres-long crocodile - believed to be an American crocodile - looks like it is closing in, a quick-thinking observer intervenes, throwing an object at the creature and stopping it in its tracks.

Manuel Carrera, who captured the video "not long ago", said locals dared not enter the waters for fear of enticing the male crocodile, which feeds off food left by tourists and fishermen.

However, the swimmer seemed oblivious to the danger.

"Unfortunately, that crocodile already associated us with food and as the video shows the boy was saved because the crocodile is well fed and chased at a pace that allowed him to reach the shore," he said.

Mr Carrera said he hoped the footage would serve as a warning to others and urged tourists to refrain from feeding the wildlife.