Christchurch's Lyttelton Port had to suspend the delivery of coal on train wagons on Thursday after safety concerns were flagged by a Worksafe New Zealand inspector.
The port has been plagued by safety issues over recent months including the death of a watersider who was hit by a crane just before Christmas and that of a forestry worker a month earlier.
The latest problem involved the lack of protection for workers on a conveyer belt used to load West Coast coal onto ships.
This saw the port closed to coal trains for 18 hours from Thursday afternoon while temporary safety fences were installed.
A Worksafe New Zealand spokesperson says the port is subject to a further three prohibition notices which prevent work from being carried out in other areas of the port until safety concerns are addressed.
Following the deaths of two workers last year and the serious injury of another in January, the South Island port company was been issued with a total of five worksafe improvement notices from the Ministry of Business, Innovation and Employment (MBIE).
Site safety inspectors found the company had been allowing empty containers to be stacked up to seven high at its dry dock in Ferrymead, meaning either strong winds or earthquakes could cause a collapse.
In the January incident, a forklift driver was seriously injured when he was crushed by containers that fell onto his machine at the depot.
The inspectors also found containers were hazardously stacked up against neighbouring fences or were on uneven ground and were misaligned, both practices endangering passers-by.
The ministry said the port had also failed to ensure the safety of workers by not having any speed limit or directional signage at the depot, and said operators were moving at dangerous speeds.