Covid-19 patient levels in England are at their highest since the end of July with health experts warning of "sustained increases" in infections and admissions.
The number of deaths where coronavirus is mentioned on a person's death certificate are also starting to rise, says the UK Health Security Agency.
The figures come as more than half of people aged 75 and over in England have now received an autumn booster dose of a Covid-19 vaccine, with bookings opening on Friday for everyone aged 50 and above.
A total of 10,608 patients testing positive for coronavirus were in hospital as of 8am on October 12, according to NHS England.
This is up 10% from 9,631 a week earlier and is the highest figure since July 29.
Patient numbers topped 14,000 in mid-July at the peak of the wave of infections caused by the Omicron BA.4 and BA.5 subvariants of the virus, then fell steadily until mid-September.
Numbers have risen in recent weeks, signalling Covid-19 is once again becoming more prevalent.
However, the rate of increase has slowed in recent days.
The jump of 10% in the seven days to October 12 is much lower than the rise of 37% in the seven days to October 5.
Covid-19 hospital data is currently published once a week on a Thursday.
The latest figures show most regions are continuing to see a rise in patients, though levels have fallen slightly in north-west England and south-west England.
All numbers remain well below those reached during the early waves of the pandemic.
Around two-thirds of patients in hospital who test positive for Covid-19 are being treated primarily for something else.
But they need to be isolated from patients who do not have the virus, putting extra demands on staff already struggling to clear a record backlog of treatment.
The rate of Covid-19 hospital admissions stood at 12.6 per 100,000 people in the week to October 9, up from 10.7 the previous week.
Rates are highest among people aged 85 and over at 151.7 per 100,000.
This is up from 130.3 and is the highest rate for this age group since mid-July.
Dr Mary Ramsay, director of public health programmes at the UK Health Security Agency (UKHSA), said: "We're seeing sustained increases in Covid-19 cases and hospitalisation rates, so we continue to urge those eligible for vaccinations to come forward, whether that's a first dose or a booster.
"Vaccines are the best protection against severe disease and hospitalisation this winter and it's never too late to take up your first dose.
"There are early indications that deaths with Covid-19 have also started to rise. Whilst this is concerning, it is too early to say whether these are deaths due to Covid-19 and it is reassuring that at this stage there is no overall excess mortality.
"If you are unwell or have symptoms of a respiratory infection, it is particularly important to avoid contact with elderly people or those who are more likely to have severe disease because of their ongoing health conditions."
Separate figures published on Thursday showed the number of people in England waiting to start routine hospital treatment stood at seven million at the end of August, a new record high.
Professor Sir Stephen Powis, NHS national medical director, said the increase in patients with Covid-19 was causing "continued pressure" on the health service, along with a rise in the most serious ambulance call-outs and delays in discharging patients into community and social care.
He added: "As we prepare for a difficult winter ahead, it is vital that people protect themselves by coming forward for Covid and flu vaccinations if they are eligible as soon as they can - with bookings opening on Friday to everyone aged 50 and over."
More than half (51.1%) of people aged 80 and over in England are now likely to have received an autumn booster dose of Covid-19 vaccine, along with a similar proportion (52.1%) of 75 to 79-year-olds.
The booster is intended to increase protection against serious illness during the next waves of the virus.
The UKHSA data, which covers vaccinations up to October 9, also shows that 45.9% of 70 to 74-year-olds are estimated to have had the booster, as well as 37.7% of people aged 65 to 69.
All people aged 50 and over will be able to book an appointment for the booster from Friday providing they had their last jab at least three months ago.
Doses are also available to frontline health and care workers, pregnant women and people with weakened immune systems.
Figures published last week by the Office for National Statistics confirmed that infections are on an upwards trend in England.
The number of people in private households testing positive for coronavirus in the week to September 24 was 1.1 million, or around one in 50 - up from 857,400, or one in 65, in the seven days to September 17.
Infections in England peaked at 3.1 million during the summer BA.4/BA.5 wave.
