World health bosses have elevated the coronavirus outbreak from an epidemic to pandemic.

The World Health Organisation (WHO) director-general Dr Tedros Ghebreyesus announced on Wednesday that the number of cases of Covid-19 outside China has increased 13-fold in the past two weeks, and the number of affected countries has tripled.

The Centre for Disease Control and Prevention (CPD) defines a pandemic as an epidemic that has spread over several countries or continents, usually affecting a large number of people.

On Wednesday, the UK saw its highest single-day leap in positive cases rising by 83 to 456. There have been eight confirmed deaths as a result of the virus.

Norfolk is one of 12 counties that has no confirmed cases of the virus.

Read more: Norfolk coronavirus campaign targets children with hand washing messageToday, the prime minister will chair an emergency COBRA at Downing Street where ministers will discuss whether to shift its response to the disease from the 'containment' phase to the 'delay' phase.

If this is carried out it would see more stringent social distancing measures introduced, such as restricting public gatherings and wider spread advice for people to self-isolate.

Read more: Coronavirus: Public gatherings could be restricted as government set to move to 'delay phase'Dr Ghebreyesus said: 'Pandemic is not a word to use lightly or carelessly. It is a word that, if misused, can cause unreasonable fear, or unjustified acceptance that the fight is over, leading to unnecessary suffering and death.

Describing the situation as a pandemic does not change WHO's assessment of the threat posed by this virus. It doesn't change what WHO is doing, and it doesn't change what countries should do.

We have never before seen a pandemic sparked by a coronavirus. This is the first pandemic caused by a coronavirus.

And we have never before seen a pandemic that can be controlled, at the same time.'

The director-general called on countries to take 'urgent and aggressive action' and that several countries had demonstrated the virus can be suppressed and control.

Across the world, 81 countries have not reported any cases, and 57 countries have reported 10 cases or less.

Dr Ghebreyesus said: 'We cannot say this loudly enough, or clearly enough, or often enough: all countries can still change the course of this pandemic.

'If countries detect, test, treat, isolate, trace, and mobilize their people in the response, those with a handful of cases can prevent those cases becoming clusters, and those clusters becoming community transmission.

'Even those countries with community transmission or large clusters can turn the tide on this virus.

'Several countries have demonstrated that this virus can be suppressed and controlled.

'All countries must strike a fine balance between protecting health, minimizing economic and social disruption, and respecting human rights.

'We're in this together, to do the right things with calm and protect the citizens of the world. It's doable.'

Read more: East of England reaches 32 cases as UK sees largest single-day rise in coronavirus cases