Ingredients thought to have caused a mass outbreak of food poisoning on Saturday at a Siem Reap province event organised by the NGO World Vision were seized yesterday and sent to Phnom Penh to undergo tests.

A crowd of more than 700 people, mainly comprising schoolchildren, attended the event in Chi Kraeng district, which focused on raising awareness about child labour. But free snacks organised by the NGO – a baguette filled with meat and pickles – left the majority unwell.

Siem Reap Provincial Governor Khem Bunsung said 542 people, including 364 children, had fallen ill. He added that most had been quickly discharged from hospital, with just 30 people remaining at health centres yesterday afternoon.

However, Um Sareth, the head of a health centre in Pongro Loeu commune, said the real number was much higher, with more than 800 people reporting symptoms of food poisoning.

Soeun Sen, chief of Siem Reap’s anti-economic crimes police unit, said officials yesterday ordered the temporary closure of the bakery that supplied the bread.

Loaves of bread were seized from the Ponleur Preah Atith bakery and sent to Phnom Penh to undergo tests.

“All the ingredients – chilli sauce, bread, and pickles – were sent to checkpoint officials who forwarded them to a laboratory in Phnom Penh, but the result has not come out yet,” Sen said.

“The bakery has to be closed temporarily while we wait for the laboratory’s result,” he added.

According to Sen, the bakery has been operating without a licence since June 2014, but the owner claims he has filed an application and is awaiting approval.

Speculation was rife yesterday about what caused the food poisoning, with herbicides, unhygienic handling of the food, and out of date ingredients all cited as potential culprits.

Poeng Visal, a teacher at Kbal Domrey primary school, was among the hundreds who fell ill after eating the snack.

“After I had the meat sandwich, I got a fever and vomited and then I got diarrhoea,” he said. “I suspect that the [flour] might have expired.”

In a statement yesterday, World Vision said that a “thorough internal investigation will take place in conjunction with the local police investigation and the findings will help World Vision put in place specific measures to ensure that food that is provided at World Vision events [is] safe for consumption”.

Channpheaktra Hong, a World Vision public relations officer, said the sandwiches were prepared by a youth group that regularly caters local events, and donates the proceeds to vulnerable people in the community.

“This is not the first time we [have used their] services, and there haven’t been any problems in the past,” he said.

He added that the NGO would wait for official results from the tests before deciding whether to continue working with the Ponlok Thmey youth group, but, “based on our experience with them, we will continue to support them”.

Hong added that preliminary investigations into the contaminated food had suggested it was the result of herbicides on the pickle.

But Dim Theng, lab director at CamControl, one of the Ministry of Commerce’s departments leading research into food safety, said it was likely that those preparing the food were behind the contamination. “Based on my experience, I think it was a hygiene problem, not a technical problem,” he said.

Srey Oeuy, a representative of Ponlork Thmey, declined to answer questions yesterday about measures taken to ensure hygiene standards.

The incident is just the latest outbreak of food poisoning in the Kingdom, which experts say is due to a lack of a stringent food-safety regime.

A food law, which has been in the works since 2004, is currently being drafted. It aims to regulate food safety and quality in Cambodia.

Theng of CamControl said the importance of the law, which is set to be complete by the end of the year, cannot be underestimated.

He said that the new legislation aims to control food “from the farms to the table”.