Kenyan police have fired tear gas at children protesting against the seizure of their school playground by a property developer.

Around 100 primary schoolchildren and a small group of activists pushed over a newly built wall that separated playing fields and the school buildings, close to the capital Nairobi's main domestic airport on Monday.

Around 40 armed police accompanied by dogs dispersed the protesters by firing tear gas canisters, an Agence France-Presse news agency photographer at the scene said.

Dozens of children were caught in choking clouds of tear gas before being forced to shelter on a pedestrian bridge over the main road to escape the fumes.

Macharia Njeru, chairman of the Independent Policing Oversight Authority, said the incident would be investigated.

"Teargassing children is inexcusable," he said.

Well-known local activist Boniface Mwangi told Al Jazeera from Nairobi that a "school playground is a necessity, not a privilege.” Mwangi was present at the scene and witnessed the confrontation between schoolchildren and police.