A curfew in Christchurch city centre began at 7pm on Sunday and will go on until 7am on Monday.
Canterbury police superintendent commander, Dave Cliff, says the CBD is still dangerous and needs to be kept secure. He says Saturday night's curfew proved its worth.
"We had incidents where known criminals tried to impersonate tradespeople and city council officials, to access the cordoned-off area, so we are being diligent about checking the credentials of individuals going into the area."
Rubble is being removed and the clean-up is progressing although authorities warn it could be months before the CBD and other parts of Christchurch are returned to normal.
A state of emergency remains in place following the earthquake.
The Minister of Civil Defence, John Carter, says the army may be called into Canterbury tomorrow to relieve tired police officers.
Mr Carter says the police have been busy securing Christchurch and Kaiapoi.
He says officers have put in long hours and will need some support and back up and the army could also be involved in rebuilding efforts.