Four children - aged about two and three years old - have been "brutally stabbed and killed" at a nursery school in the Ugandan capital, Kampala, police said.

The three boys and a girl were killed instantly, said a police spokesperson, who added that the suspect had used more than one knife during the morning attack.

A 39-year-old man has been detained and is being questioned as "investigations continue to establish his motive, background, and any other relevant circumstances surrounding this heinous crime", according to a Uganda Police Force statement on X.

Angry parents had tried to lynch him before he was detained, news agency AFP quotes police spokesperson Racheal Kawala as saying.

Videos of the aftermath being shared on social media show images of crowds of angry and distressed people, some believed to be parents seeking news of their children.

Kawala said the suspect had recently visited the Ggaba Early Childhood Development Program School to enquire about enrolling a child and was told to return on Thursday.

"He paid for admission [and] after that proceeded and attacked these children, killing four of them instantly," she said. The killings happened before 11:00 local time (08:00 GMT), which was when the police responded to a distress call.

The other 10 children who were in the school at the time have been handed back to their parents, she added.

Investigators are at the scene in the upmarket Ggaba suburb and Kawala said more details would be provided later. Police chief Abas Byakagaba has visited the school and urged the public to remain calm while the police continue to do their work.

As sunset approached, the mood outside the school, where some staff had gathered and which remained cordoned off, was sombre.

The tragic incident has sent shock waves across the country, raising serious concerns about the safety of learners in the East African nation.