The Bolton NHS Foundation Trust medical director said a majority of the sick patients had not been vaccinated but would have been eligible for the jabs.
Dr Francis Andrews urged everyone in the area who was offered the vaccine to have it.
He said: “Whilst the numbers of people in the hospital with Covid-19 are still currently low compared to previous peaks, we have seen a modest increase in patients admitted with confirmed Covid-19 over the last week. A small number are requiring intensive care.
“The increase in admissions is seen across the age range from 35-65. The majority of patients have not received a vaccination dose, but many would have been eligible.”
Bolton has seen a 97 per cent jump in coronavirus cases over the last seven days, with the total number of cases reaching 473 on Thursday.
Scientists have called for ‘surge vaccinations’ in the affected areas to try and curtail the spread of the Indian variant, designated B1.617.2 which is thought to be more transmissable than the dominant Kent variant which emerged in England last year.
The government has said 3,500 extra Pfizer-BioNTech vaccine doses will be sent to Blackburn-with-Darwen council from next week.
Staff working at the hospital told The Independent more Covid patients had been admitted via A&E in recent weeks.
The Independent understands around 20 Coronavirus patients are being treated by the hospital, up from 11 on 27 April.
One doctor said: “I think it is already going off locally. Lots of resources going into BL3 postcode. It's a race between the vaccination of the younger age groups and the seemingly increased transmissibility of the Indian variant playing out, and as with every other wave social deprivation is going to be a key determinant.”
Coronavirus patients at The Royal Bolton Hospital are being kept on a single ward or ‘cohorted’ together to try and limit the spread of the virus within the trust.
Dr Andrews added: “It is essential that everyone who is being offered the vaccine has it, as it offers excellent protection against Covid-19. We urge everyone to continue to follow the latest government guidance. Everyone must get tested if they develop symptoms or have come into contact with a someone who has tested positive, or if they are asked to take part in screening.
“It is crucial that everyone continues to wear masks and maintain social distancing. All of these measures will help prevent further spread of Covid-19 and illness.”