The Christchurch Earthquake Recovery Authority (CERA) says the entire central city cordon may not be lifted until mid-April.
The recovery strategy, which CERA released last year, initially had a 1 April target for the lifting of the cordon.
CERA's general manager of operations, Warwick Isaacs, says the delay is because more buildings are being found to be damaged than was initially expected.
Mr Isaacs says the 23 December quake set one of his teams back by six to eight weeks.
He says buildings had to be rechecked following the December aftershock, which took a lot of time.
Mr Isaacs says it will now not be possible for the entire cordon to be lifted by April, although it will be significantly reduced from what it is now.