Warning that there will be no return to the old normal, the World Health Organisation (WHO) has urged people everywhere to play a part in preventing further spread of the coronavirus as global cases have surpassed 15 million, with nearly 620,000 deaths.

Most cases, or 10 million, were in just 10 countries, with the United States, Brazil and India accounting for nearly half, WHO, the Geneva-based UN agency, said. On Thursday afternoon, the US passed the milestone of four million infections.

"We're asking everyone to treat the decisions about where they go, what they do, and who they meet with, as life-and-death decisions because they are," WHO chief Tedros Adhanom Ghebreyesus said, speaking from Geneva.

"It may not be your life, but your choices could be the difference between life and death for someone you love, or for a complete stranger."

COVID-19 has disrupted the lives of billions across the globe, and Tedros said it is understandable that people want to get on with their lives.

"But we will not be going back to the old normal. The pandemic has already changed the way we live our lives. Part of adjusting to the new normal is finding ways to live our lives safely," he advised.