Parents of children allegedly given sedatives by staff at a preschool in Taiwan have been protesting the government's slow response to the incident.

On Sunday, hundreds of people gathered in New Taipei City to criticize the fact that it took weeks for local authorities to carry out medical tests on the children after suspicions were raised in mid-May.

On May 14, three parents told local police that their children were irritable and showed self-harming behaviors between February and April this year. They said the children told them their teachers had given them drugs, Taiwan's official Central News Agency (CNA) reported.

Medical tests uncovered traces of barbiturates and benzodiazepines -- two types of central nervous system depressant -- in some of the children.

The District Prosecutors Office in New Taipei City was first notified of a case involving the potential drugging of minors on May 15. Three days later it directed the police to search the kindergarten, retrieving CCTV recordings and other evidence, according to a statement.

As of early June, more than a dozen parents had reported the matter to the police, CNA reported, and on June 5 city authorities offered drug tests to every child attending the preschool.

As of June 8, tests of 28 children from the school, which has 67 students, found that eight had traces of barbiturates in their systems, the New Taipei City Government said.

Among those students, 16 were given drugs tests organized by the city's Education Bureau on June 5, while parents had also taken their children to local hospitals for testing prior, according to CNA.

According to Lin Ching-feng, director of the government-affiliated medical management association, 29 children had been admitted to the hospital for organized tests as of June 15, with 28 testing negative for the drugs. Confirmation of the one case was still pending at that time.

The tests were conducted weeks after the allegations of drugging.

The local education department has ordered the kindergarten to close, and has fined it 150,000 New Taiwan dollars (around US$4,850).

The principal and seven teachers were released on bail earlier this month after being brought in for questioning by authorities, CNA reported. It's not clear if they were charged for any specific offenses.

The alleged incident has created an uproar in Taiwan, and the fallout could affect the Taiwanese presidential election in January 2024, with the incumbent mayor of New Taipei City, Hou Yu-ih, standing for the opposition Kuomintang party.

Hou issued an apology over the incident earlier this month.

This story has been updated with additional information.