A 255g can of repellent containing concentrated capsaicin, a compound in chili peppers, was punctured by an automated machine after it fell off a shelf, according to local media.

The incident happened on Wednesday in a warehouse in Robbinsville, New Jersey, a neighbourhood on the outskirts of Trenton.

One of the 24 staff was reportedly sent to hospital in a critical condition, but on Wednesday night all the employees were expected to be released within 24 hours.

In a statement, a spokesperson for Amazon said: “A damaged aerosol can dispensed strong fumes in a contained area of the facility. The safety of our employees is our top priority, and as such, all employees in that area were relocated to safe place.”

The employees were hospitalised “as a precaution”, the spokesperson said.

The incident has again shone a spotlight on conditions in Amazon’s warehouses, which have attracted criticism in the US and the UK for poor working practices and a focus on productivity above worker safety.

A Guardian investigation in June detailed multiple instances of workers left unable to work following injuries sustained in Amazon warehouses, including the Robbinsville fulfilment centre.

Stuart Appelbaum, the president of the Retail, Wholesale and Department Store Union, said: “Amazon’s automated robots put humans in life-threatening danger.”

He continued: “This is another outrageous example of the company putting profits over the health and safety of their workers, and we cannot stand for this. The richest company in the world cannot continue to be let off the hook for putting hard working people’s lives at risk.”

Bernie Sanders, the US senator who ran for the Democratic presidential nomination in 2016, is among the politicians who have raised concerns about Amazon’s work practices and low pay.

In the UK ambulances were called to Amazon warehouses 600 times between 2015 and 2017. The company has denied that it had poor working conditions.

Jasper Jolly