Armed police have been deployed after shots were fired at a mosque where hundreds of people were praying near Hagley Park in Christchurch.

An eyewitness inside the mosque says he heard shots fired and says at four people were lying on the ground and "there was blood everywhere".

An eyewitness says a man wearing a helmet and glasses and a military style jacket opened fire inside the mosque with an automatic weapon.

About 300 people were inside the mosque for afternoon prayers.

People in central Christchurch have been urged to stay indoors and report any suspicious behaviour immediately to 111.

Another eyewitness said people are being evacuated from near a second mosque in Christchurch and police are swarming the area.

All Christchurch schools, Christchurch Hospital and Christchurch City Council buildings have been placed into lockdown.

RNZ