Police in Northern Ireland are investigating a bottling plant over what appeared to be human waste was discovered in a shipment of empty Coke cans.

The plant is responsible for the entire island's Coca-Cola market, UK media has reported.

The Belfast Telegraph reports that a night shift was disrupted last week when a container of cans clogged up machines, leading to the discovery that several of the cans were filled with what looked like human waste.

Workers suspected that someone had used the empty cans as makeshift toilets.

"It was absolutely horrible, and the machines had to be turned off for about 15 hours to be cleaned," a source told the newspaper.

Coca-Cola has told media organisations that it identified the matter immediately and is conducting a thorough investigation and has called in local police.

“This is an isolated incident and does not affect any products currently on sale,” the company said in a statement.

The Knockmore Hill plant employs more than 500 workers and 97 per cent of Coca-Cola products across the island of Ireland are manufactured by the plant, according to the soft drink company.