New Zealand authorities are investigating the maintenance of all the country's hot air balloons following a fiery crash last month that killed 11 people.

The Civil Aviation Authority says it's urgently reviewing all 73 balloons registered in the country after accident investigators found problems with the maintenance of the balloon that crashed.

The pilot and the five couples on board the balloon died after it hit power lines Jan. 7 in a rural part of the country about 50 miles (80 kilometers) northeast of Wellington.

Investigators say it appears a strength test and fuel system inspection were not done correctly on the balloon. They have not yet determined whether the maintenance problems contributed to the crash.