Nearly a third said patient care was compromised on each shift.
Bed occupancy was found to be "alarmingly high", with patients becoming more dependent on nursing care while in hospital.
This is set, the RCN claims, against a backdrop of half of wards not having enough qualified nurses. All wards reported that on average they have 14 per cent less staff in post than planned for.
A second survey questioning patient survey also released by the RCN found that student nurses are being left in sole charge of patients during clinical placements.
More than 1,500 student nurses from across the UK were asked about their experiences during their placements. Forty-four per cent said they had been left unattended with patients without any warning and without a registered nurse or doctor present.
Commenting on the reports, Dr Peter Carter, general secretary of the RCN, said: "This is yet another example of how deficits-driven cost cutting is compromising patient safety.
"Up and down the country, we are seeing nursing jobs being lost and posts being frozen and deleted to cut costs. That means those registered nurses left have to do ever more with even fewer resources. It also means they have even less time to devote to supporting the next generation of nurses during their clinical placements."
In response to the surveys, health minister Lord Hunt said that the 85,000 nurses recruited since 1997 are providing "safe, high quality treatment for millions of NHS patients every year".
"Patient safety is of paramount importance to government and NHS staff alike, and we would expect any nurse, whether in training or in practice, to report any incident they feel has an adverse effect on patient safety," Lord Hunt added.
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