A Virgin Australia plane had to turn back to the airport after liquid from the bathroom leaked into the aisles creating an "unbearable" smell.
The flight bound for Sydney was forced to turn back to Los Angeles after sinks on board leaked.
Julia Malley, a resident of Christchurch, where the plane was headed after Sydney, said the smell was "unbearable" in an interview with New Zealand radio, suggesting there was human poo flowing into the cabin.
Ms Malley added that passengers near the toilets were offered masks to help deal with the smell.
According to the BBC, she said: "We could see it [human waste] it go through the aisles, like it was very obvious,"
However, Virgin has denied there was leakage from the toilets onboard.
According to abc.net.au, A Virgin Australia statement said: "As the issue was with the aircraft sink, and not the toilets, there was no incident of leaked human waste."
The statement continued: "In accordance with standard operating procedures, the captain made the decision to return to port as a precautionary measure after two of the sinks on board were leaking.
"The onboard toilets operate on a completely separate drainage system."
According to Stuff.co.nz, the statement added: "All affected guests have been re-accommodated free of charge onto a recovery flight scheduled to depart Los Angeles Airport for Sydney at 19:55 local time.
"The safety of the aircraft was never in question."
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