British tourists witnessed a crocodile eating the remains of a man during a sunset cruise along a river bordering Zimbabwe and Zambia.

The shocking scene on the banks of the Zambezi River, believed to have occurred in mid-February, was spotted by the group’s guide who originally thought the reptile was feasting on another animal.

It was only when the party approached the animal that they realised his grisly meal was composed of the bottom half of a human being.

"All there was to see of him was his trousers," a local source, who did not wish to be named, told The Daily Telegraph.

On their return to the nearby camp, the guide and tourists reported the discovery to authorities. Later searches failed to turn up any remains.

There have been no reports of missing people from nearby communities, leading Zimbabwean rangers to suspect the individual may have been a poacher.

"We strongly suspect it was a poacher," conservationist Trevor Lane said.

Mr Lane, who co-founded The Bhejane Trust conservation projection, claimed that days earlier a rangers had launched a successful ambush against 13 poachers who had crossed from Zambia into Zimbabwe.

Although one man was killed, the rangers noted that only nine made it across the river to safety and three remain unaccounted for.

"Maybe he was wounded and tried to swim across the river," Mr Lane, whose conservation efforts focus in Zimbabwe's Zambezi and Hwange National Parks, told The Times Live.

Crocodile attacks are frequent in Zimbabwe. In the last three months three children have been killed after they encountered the deadly animals.