The operator of major conveyor belt sushi restaurant chain Sushiro said Wednesday it has filed a damage complaint to police against a customer after a video of them misusing and licking unused cups and sushi racked up millions of views online.

The move by Akindo Sushiro Co. comes as videos of customers' unhygienic behavior at its and competitors' restaurants, where food is served in plates that travel by conveyor belts that pass numerous diners, have attracted increasing negative attention and criticism online.

Supplied photo shows a variety of sushi at sushi restaurant chain Sushiro. (Kyodo)

In the 48-second clip widely shared on social media, a customer at a branch of the Sushiro in central Japan's Gifu Prefecture licks the open top of a soy sauce bottle, puts the rim of an unused tea cup in their mouth, and then rubs a passing plate of sushi with a finger covered in their saliva.

The operator filed the damages complaint to police on Tuesday over the video. Although the company has received a direct apology from the person shown in the footage and their guardian, it says it intends to "continue to respond strictly in both a civil and criminal capacity" to the case.

The outlet in the video has since cleaned all of the cups in the affected store, and replaced all of its soy sauce bottles, the operator said.

Customers at the restaurant and nearby outlets will also have to bring their utensils and condiments to their tables from a serving point. The company says it will also provide disinfected tableware to diners requesting them at any of its locations nationwide.

Sushiro's competitor Hama-sushi Co. said it has also filed a damages complaint to police after a video went viral in January that showed a customer applying wasabi to sushi that appears to be traveling on a belt for food ordered by other diners.

The company said it is considering filing a civil suit including claiming compensation against the individual in the clip.

The problem is spreading outside the sushi trade, too, with a video of a customer eating from a serving spoon at an outlet of udon noodle chain Sukesan Udon making its way online, the chain's operator told Kyodo News on Wednesday.

The company, whose outlets are primarily based in the southwestern Kyushu region, said it has disinfected one of its stores and is mulling how to respond further.

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