The Virgin Australia flight bound for Sydney was forced to return to Los Angeles airport after water systems broke down three hours into the journey. The stench was so unbearable that passengers seated near the toilets were given masks to wear for the remainder of the journey.

Virgin apologised for the incident, which it said had been caused by a leaking sink. However, the official explanation was pooh-poohed by passengers who insisted that a foul-smelling stream of excrement had flowed freely down the aisles after the offending loo exploded.

“We could see (human waste) go through the aisles – it was very obvious,” said passenger Julia Malley, according to the Australian Broadcasting Corporation.

Ms Malley, who lives in Christchurch, New Zealand, elaborated on the drama on her Facebook page, saying: “Stuck in LA… 3 hours into our flight they decide to turn around because the bathroom exploded and we were literally sitting in crap. 2 rows away and offered masks for the 3 hours back. YUCK!”

Virgin said the plane had turned back for the comfort of passengers and denied the leakage had been from the toilets.

“The onboard toilets operate on a completely separate drainage system,” said a spokesman. “As the issue was with the aircraft sink, and not the toilets, there was no incident of leaked human waste.”

Virgin operations manager Roger Lindeman offered his “sincere apologies” in a letter to passengers.

“Unfortunately the aircraft did need to return to Los Angeles due to an issue with the plumbing in the freshwater overflow system on board and could not continue with the journey,” said Mr Lindeman.