"Over 100 Covid-19 test kits from South Korea have just arrived. Place your orders quickly," said one seller on a social media platform as Vietnam grapples with its fourth Covid-19 wave.

At VND650,000 ($28.34), each pack has two kits with a precision rate of 99 percent. All testing procedures can be done in 15 minutes, the seller said.

She also included links to articles showing how popular these products are in South Korea.

But when a VnExpress reporter asked for more documents to confirm which company had imported these products into Vietnam, the seller could not provide the information immediately.

Another seller said that the kits had been hand-carried from South Korea because these products are not regulated and could not be imported through official channels.

Each package of two kits costs VND690,000, while a single kit costs up to VND350,000.

"Just take a sample from your nose to test and wait 15-20 minutes. One line means negative, two means positive," he said, adding that all his friends and family have used the kits.

Other kits made in China have been promoted widely on social media, but none have been authorized by the Ministry of Health.

Nguyen Dinh Anh, head of communications at the ministry, said Vietnamese citizens should not purchase the kits, because substandard quality can contribute to the spread of the novel coronavirus due to false negatives.

Market authorities have said they are investigating the sale of these products on the internet and will punish those found violating regulations.

Products that concern human wellbeing must be authorized by health officials and people should not purchase those of unclear origins advertised on the internet, said Nguyen Duc Le, deputy head of the Vietnam Directorate of Market Surveillance.

Hanoi market authorities Thursday found the first unauthorized sale of Covid-19 test kits with 29 boxes said to be from China.

Vietnam mainly uses the RT-PCR method for Covid-19 testing. Health authorities also use quick tests with a precision rate of 70-75 percent but only to increase speed of containing the pandemic in areas with high infection risks.

In the country, only two entities are authorized to produce the quick test kits – the Viet A Corporation (in cooperation with the Military Medical University) and the Sao Thai Duong (Sunstar Jsc) company.