It is ‘extremely challenging' and hospitalisations are rising rapidly in London, according to the PM.
Mr Johnson called an impromptu cabinet meeting today to evaluate new Covid-19 data.
Experts want the PM to act quickly to save the NHS, but his own top team is reluctant.
We will have to reserve the prospect of taking further action to defend the public, public health and the NHS,' he said following the meeting.
He added the data is constantly monitored ‘hour by hour' and the government ‘won't hesitate to respond'.
With the current winter wave, the PM urged people to be cautious and get vaccinated.
He claimed the cabinet had debated the issue for a few hours and that ‘the arguments are very, very balanced'.
Sir Patrick Vallance and Professor Chris Whitty, England's chief medical officer, presented the newest findings to the cabinet.
The Omicron variety is still being studied by experts, specifically how severe it is and how immunizations affect it, so Mr Johnson says there are still some questions to be answered before making any decisions.
‘We're looking at all kinds of options… we won't rule anything out,' added the PM.
Mr Johnson's decision comes after 91,743 new Covid-19 infections were reported in the last 24 hours.
The UKHSA reported 8,044 new confirmed Omicron cases, bringing the total to 45,145.
Within 28 days of testing positive for Covid-19, 44 more perished.
Following Sajid Javid's refusal to rule out action before Christmas on the BBC yesterday, fresh measures were expected to be approved at today's cabinet meeting.
Mr Johnson's cabinet is split on whether to reimpose further sanctions, with one member willing to resign.
Chancellor Rishi Sunak reportedly opposes it because of economic concerns.
While the prime minister can take measures without legislative consent, enacting new legislation may cause a political crisis.
Recently, around 100 Tory backbenchers refused to vote for Plan B measures, the greatest revolt since Mr Johnson took office.
‘Pleased the Cabinet and PM are now listening to their backbench MPs & for once pushed back on the scaremongering by the lockdown extremists,' Esther McVey, one of the Covid rebels, tweeted following the PM's interview.
‘The 100-strong backbench mutiny last week looks to have helped.'
‘Health leaders are not pushing for greater limitations as they know these may be highly harmful to people's health and wellbeing, but with the mounting incidence of coronavirus and the quick spread of Omicron, they fear they will be needed soon.'
‘If the Plan B measures and boosters aren't adequate, they expect the government to act fast and preemptively in the national interest.'
This includes summoning Parliament back after Christmas if necessary.
‘This is about safeguarding public health and decreasing disease,' he added.
The PM has come under criticism today when a picture emerged of him and Carrie drinking wine in the yard with Downing Street staff during a social mixing restriction.
The image was of ‘people at work, talking about work', Mr Johnson said after the cabinet meeting.