Demolition of the chimney at Christchurch hospital is underway.
The 45-year-old structure, near the corner of St Asaph and Antigua streets is cracked. Engineers have assessed it as being at high risk of collapse in further earthquakes.
Canterbury District Health Board chief executive David Meates says a non-compliant chimney has been installed in the interim in order to keep the boilers going to provide a continuous supply of steam.
Work is expected to continue until mid-February, with partial road closures in the immediate vicinity.