The government is "absolutely confident" the UK will have 800,000 coronavirus vaccine doses by next week, when the vaccination programme starts, the business secretary has said.
Alok Sharma said some of the Pfizer/BioNTech doses had arrived, with more expected by the end of the year.
He was unable to say how many that will be.
NHS Providers said the UK must work on the basis that more doses beyond this might not arrive "for some time".
Chief executive Chris Hopson tweeted that it was "vital" hospitals sought to vaccinate as many people as possible in the highest priority groups.
He added that with "every day that goes past, we become more confident we will get a lot more [doses] and get them soon".
It comes as official data showed infection levels were falling in all English regions, except the North East.
The government said the R number - the average number of people each person with Covid-19 goes on to infect - has fallen to between 0.8 and 1 in the UK, from between 0.9 and 1 last week.
It also reported that a further 504 people had died within 28 days of a positive Covid-19 test, bringing the total number of deaths in the UK to 60,617.