Saffron Cordery, deputy chief executive of NHS Providers, said the number of coronavirus patients in hospital on ventilation beds had increased by 41 per cent in the last week to 227.
It was a strong indication coronavirus was having an impact on health services, Xinhua news agency quoted Cordery as saying to the BBC on Wednesday.
"Trusts on the frontline are really coming under huge pressure, they have plans in place to tackle the backlog, but with more Covid cases and demand for emergency care going up, that's really challenging."
Cordery said NHS leaders were very concerned about a potential surge that could collide with other winter illnesses such as flu and respiratory viruses later in the year, posing "a significant challenge" to the health system.
"I think we need to look at this sudden rise in the demand for emergency care as well, so you know we are seeing record levels of demand for that kind of care."
The UK has so far reported 4,683,925 coronavirus cases and 128,291 deaths.
The latest available data showed the number of patients in hospital at 1,378, similar to early May, but still below the peak of 4,077 on January 24.
Meanwhile, recent data published by the Public Health England showed the AstraZeneca vaccine is 92 per cent effective against the Delta variant after two doses, and the Pfizer vaccine is 96 per cent effective after two doses.