WHO director Dr Tedros Ghebreyesus claimed the spread of the virus was actually speeding up, despite lockdowns being loosened around the world.
He said countries like South Korea, China, Germany, Singapore and Japan had shown there is a blueprint to suppressing the disease.
Earlier this month the WHO urged Britain not to lift lockdown until its test and trace system was up to scratch, after it emerged a third of patients were being missed.
The UK Government has been criticised for its top-down response to the outbreak and refusal to give responsibilities to local public health bodies.
During a virtual news conference from the WHO’s Geneva headquarters yesterday, Dr Tedros said: ‘Although many countries have made some progress, globally, the pandemic is actually speeding up.
‘We all want this to be over. We all want to get on with our lives, but the hard reality is that this is not even close to being over.
‘Some countries have now experienced a resurgence of cases as they start to reopen their economies and societies. Most people remain susceptible. The virus still has a lot of room to move.
The worst is yet to come. I’m sorry to say that, but with this kind of environment and condition, we fear the worst.’
He added: ‘And that’s why we have to bring our acts together and fight this dangerous virus together.
Dr Tedros praised Japan for managing to have one of the lowest death rates in the world despite having one of the oldest populations of any nation.
The virus has infected more than 18,476 people in Japan, but has killed less than 1,000 people.