MIDDLE schools in the Dutch university city of Leiden will remained closed on Monday after police said they had received a "serious threat" of a shooting being planned at one.

"Police have received mention about a possible school shooting (being planned) in Leiden," said a statement issued late on Sunday evening.

"In light of this serious threat, it has been decided not to take any risk and therefore all middle schools will remain closed on Monday," the statement added.

Police said they did not yet know who had made the threat, which was posted on a website, or which school had been targeted.

Pupils and their parents hade been warned to stay home and an intensive investigation was under way, police said.

Middle schools in the Netherlands cover the 12-to-16 age group and in Leiden there are at least 22 such schools - some of them international. The city, which also hosts the country's oldest university, lies just northeast of The Hague.

In April 2011, a man armed with a semi-automatic rifle killed six people and wounded at least 10 others when he opened fire on shoppers in a mall at the nearby town of Alphen aan de Rijn.

Gunman Tristan van der Vlis, 24, then committed suicide, in what was the worst mass shooting in recent times in the Netherlands.

In 1999, four students and a teacher were wounded when a student fired 10 shots in a computer room at a school in the southern Dutch town of Veghel.