A lunchtime brawl between 145 Kazakh and Chinese workers in a canteen at Kazakhstan's Aktogay copper mine saw 65 taken to hospital, and as of Friday, 31 remained as in-patients.

The fight broke out when a Chinese worker complained about the quality of food and the small size of portions, Tengrinews, an English-language news portal reported.

Chinese workers began loudly expressing their dissatisfaction, ignoring the efforts of their supervisor to calm down, according to police.

Security staff tried to calm the situation and took the complaining workers from the canteen before a large fight broke out with Kazakhs smashing up the Chinese workers' dormitory after the fighting in the cafeteria.

The Aktogay mine is in eastern Kazakhstan, about 250 km from the Kazakh-Chinese border. The project includes an open-cast mine and a concentrator producing copper cathode from oxide ore and copper concentrate from sulphide ore that also contains some valuable molybdenum as a by-product.

Around 150 Chinese and 400 Kazakh workers are employed at the site after Non Ferrous China was awarded a contract for the construction of the sulphide concentrator last year.

Kazakhstan's Foreign Ministry said it was conducting a thorough investigation into the circumstances of the incident, according to Tengrinews.

It also confirmed it was cooperating with the Chinese Embassy in Kazakhstan. "We are confident that all perpetrators from both sides will be held responsible according to the law," the ministry said.

Kazakh vice-prime minister Berdibek Saparbayev confirmed that 31 men remain in hospital in Ayagoz town and Ust-Kamenogorsk city. "Their condition is moderate, none sustained grave injuries," he said, adding that the incident was simply "domestic violence", emphasizing that it had no political or inter-ethnic basis.