Gunshots have been heard near a mosque in Christchurch, New Zealand, local media report, as police warn of a "critical incident".

Witnesses told local media that several people appeared to be injured inside the mosque. Police have warned people to avoid the area.

All schools in Christchurch have been placed on lockdown, police commissioner Mike Bush said.

Media reports say that armed police are clearing buildings in the vicinity.

The incident is said to have taken place at the Al Noor mosque, located in central Christchurch along Dean Avenue facing Hagley Park.