The WHO said there are now 300,000 confirmed cases worldwide. The first 100,000 were reported in the first 67 days of the virus, the second 100,000 cases came 11 days later and the next 100,000 cases just four days after that, the global health body said.
WHO director general Tedros Adhanom Ghebreyesus said there were also "alarming" reports of health workers getting sick.
He said he would be contacting the G20 heads of state to solve the global shortage of protective gear for health workers.
"More than 300,000 cases of COVID-19 have now been reported to WHO, from almost every country in the world," he told a press briefing in Geneva in Monday.
"The pandemic is accelerating ... but we're not prisoners to statistics. We're not helpless bystanders.
"We can change the trajectory of the COVID-19 pandemic."
Dr Ghebreyesus said asking people to stay home and other physical distancing measures were important to slow the coronavirus, but stressed they were defensive measures.
"To win, we need to attack the coronavirus with aggressive and targeted tactics - testing every suspected COVID-19 case, isolating and caring for every confirmed case, and tracing and quarantining every close contact," he said.
He acknowledged that measures put in place to slow the spread of the virus may have unintended consequences by exacerbating shortages of essential protective gear.
"I will be addressing heads of state from the G20 countries," he vowed.
"I will be asking them to work together to increase production, avoid export bans and ensure equity of distribution on the basis of need."
Meanwhile, the global health body said a decision would be made about the future of the Tokyo 2020 Olympic Games soon.
"We are feeding into the IOC (International Olympic Committee) and the Japanese government and the Tokyo 2020 Committee's deliberations on this and I believe a decision will be made very soon regarding the future of the Games," executive director of the WHO's Health Emergencies Program Michael Ryan said.
"The decision to postpone the games would be purely a decision of the Japanese government and the IOC but we are in the process of offering them risk advice.
"As we have said previously, we have every confidence that the Japanese government and the IOC would not proceed with any games should it be dangerous to athletes or spectators."