Daryl Lehmann was on the South Alligator River with his family on Sunday when his grandsons spotted some vicious croc activity.

"They said, 'look at those crocs' and I quickly got the phone out," Daryl Lehmann told 9news.com.au.

Estimating one of the crocodiles to be "at least four metres long," Lehmann filmed the predators approach a dead buffalo floating in the water.

Clearly feeling more than a little snappy, the crocs turn on each other and lock jaws as they thrash in the water.

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After a brief but vicious brawl, the animals disappear in to the water.

Nearly 30,000 social media users have viewed Mr Lehmann's footage on Facebook.