British Prime Minister Boris Johnson on Monday chaired a meeting of the government's COBRA emergency committee amid rising threat of the novel coronavirus as Britain confirmed four new COVID-19 cases on the same day, bringing its total number of infections to 40.

During the meeting, a four-stage "battle plan" was agreed by ministers, which lays out in detail the measures that could be used if and when they are needed.

At the moment the situation is at the "containment" stage, but this may change depending on scientific advice, said Johnson, noting that the coronavirus outbreak is likely to become more significant in the coming days or weeks.

"We have also agreed a plan so that if and when it starts to spread, as I'm afraid it looks likely it will, we are in a position to take the steps necessary to contain the spread of the disease as far as we can, and to protect the most vulnerable," he said.

"There now seems little doubt that coronavirus will present a significant challenge for our country. But we are well prepared, and the government and the NHS (National Health Service) will stop at nothing to fight this virus," said Johnson.

He emphasised the need for the public to help by hand-washing and cover mouth and nose with a tissue when cough or sneeze.

Johnson's government and the devolved governments in Scotland, Wales and Northern Ireland will launch a major public information campaign Tuesday, giving details of the four stages of the battle plan.

Downing Street also set up a "war room" in the Cabinet Office in Whitehall, which will bring together communications experts from across the government and top experts from the NHS to roll out a public information campaign and respond quickly to cross-cutting issues.

Asked about moving up to the next level, Johnson did not go into detail about what measures may be introduced, noting that the most important thing for people to understand is that measures will be guided by scientific advice.

"Our job is to protect the public and we have a very good plan to take the steps necessary to stop the spread. We will be guided by scientific advice," said Johnson.

Local media reported that if the situation worsens, the government may recall retired doctors and nurses to help treat and nurse COVID-19 patients, cancel large scale events, curb public transport networks, close schools and in a worst case scenario, close major cities.

COBRA, or COBR, meetings are named after Britain's Cabinet Office Briefing Room A on Whitehall, gathering ministers, civil servants, the police, intelligence officers and others appropriate to whatever they are looking into in an emergency response.