Amazon's staff are falling asleep on their feet and being taken away in ambulances as they struggle to meet warehouse targets, an investigation has claimed.

Cameras monitor every move as employees try to process up to 300 items an hour, it has been alleged. Screens remind them if they are falling short.

Exhausted staff are said to cover clocks so they are not reminded how long there is to go on their shifts, and have to walk up to a third of a mile to use the toilet.

The claims in a newspaper were made about the online retailer’s newest warehouse – which the company refers to as a ‘fulfilment centre’ – in Tilbury, Essex.

The packing plant is the biggest in Europe, the size of 11 football pitches, and is due to ship 1.2million items this year.

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Amazon's staff are falling asleep on their feet because of extremely tough working conditions

Amazon workers were seen asleep on the job as they complained about intolerable working conditions at the firm's Tilbury warehouse

But the investigation, by an undercover reporter for the Sunday Mirror who spent five weeks there, suggested workers suffer mentally and physically as they try to meet demand.

He said that some of his colleagues were so tired from working 55-hour weeks that they would ‘sleep on their feet’.

‘Those who could not keep up with the punishing targets faced the sack – and some who buckled under the strain had to be attended by ambulance crews,’ he added.

It comes at a time when Amazon has promised to improve the treatment of staff following accusations of poor conditions and low pay.

Workers in Italy and Germany have gone on strike in protest at their workloads.

But one worker in Tilbury reportedly complained: ‘At my induction, someone was asking why the staff turnover was so high. It’s because they’re killing people. All my friends think I’m dead. I’m exhausted.’

Staff complained about the state of the toilet in the Tilbury warehouse in Essex (pictured)

Another is said to have written on a whiteboard for staff comments: ‘Why are we not allowed to sit when it is quiet and not busy? We are human beings, not slaves and animals.’

Amazon said yesterday: ‘Amazon provides a safe and positive workplace with competitive pay and benefits. We are proud to have created thousands of roles in our UK fulfilment centres. As with most companies, we expect a certain level of performance.

‘Targets are based on previous performance achieved by our workers. Associates are evaluated over a long period of time.’

The retailer made £7.3billion of sales in the UK last year and employs 24,000 people.

Staff who buckle under the pressure are taken away in ambulances, it was claimed

The Essex plant has no natural light, so staff cannot see whether it is day or night outside. The undercover reporter worked from 7.30am to 6pm with two half-hour breaks, giving just enough time to race to the canteen for food.

One colleague is said to have collapsed as they worked and was taken to hospital by ambulance. Another was seen by paramedics after suffering a panic attack when she learned compulsory overtime meant she would have to work up to 55 hours a week over Christmas.

One worker told the paper: ‘Everybody suffers here.’ They added that staff reported a variety of stress-related injuries, including pulled hamstrings and ligaments.

Once items are picked they go to a packing area where workers prepare 120 items for shipping every hour – rumoured to be increasing to 200 – or 85 multiple items, according to the investigation.

This board showed some of the staff's grievances at the Essex warehouse, including complaints about the 'disgusting' toilet

Shifts begin at 7.30 in the morning and finish at 6pm, with workers given just two half-hour breaks during the day

Many patrolled conveyor belts looking for smaller items to keep up their average.

Amazon has also defended itself after it was revealed that ambulances were sent to its main Scottish warehouse 43 times last year.

Emergencies included 15 of the most serious Category A classification, with 23 workers taken to nearby hospitals. Call-outs to the depot in Dunfermline involved two staff being treated for falls, a call about ‘traumatic injuries’ and two for ‘industrial accidents’.

An Amazon spokesman said: ‘Independent safety experts certify our compliance with all relevant laws and regulations.’