A TV grab taken from the World Health Organization website shows WHO Chief Tedros Adhanom Ghebreyesus via video link as he delivers a news briefing on COVID-19 (novel coronavirus) from the WHO headquarters in Geneva on March 30, 2020.

World Health Organization officials warned nations across the globe against lifting government lockdowns to contain the Covid-19 outbreak too soon, saying that the coronavirus spreads fast and is 10 times deadlier than the 2009 flu pandemic.

"While Covid-19 accelerates very fast, it decelerates much more slowly. In other words, the way down is much slower than the way up," WHO Director-General Tedros Adhanom Ghebreyesus said at a press conference at the organization's Geneva headquarters on Monday. "That means control measures must be lifted slowly and with control. It cannot happen all at once."

U.S. political leaders, from President Donald Trump to New York Gov. Andrew Cuomo, have said they hope to reopen businesses as soon as it is safe to do so.

The coronavirus, which emerged in China over three months ago, has infected more than 1.8 million people worldwide and killed at least 115,000 people.

"Control measures can only be lifted if the right public health measures are in place, including significant capacity for contact tracing," Tedros said.

Tedros outlined a checklist for countries before they should consider lifting social distancing measures:

Transmission of the virus should be controlled.

A surveillance system should be in place to detect, isolate and treat patients.

Outbreaks in hospitals and nursing homes should be minimized.

Preventive measures in essential locations such as schools and workplaces should be in place.

The risk of importing the disease from abroad should be under control.

WHO was asked about using hydroxychloroquine, which is being tested in New York state and has been touted by Trump as a "game-changer" in treating Covid-19 even though the drug has not been put through a rigorous clinical trial.

WHO officials said they are "eagerly" awaiting results from randomized controlled trials seeing whether hydroxychloroquine is effective in fighting the coronavirus, adding that there is currently no evidence it works.

"There is no empirical evidence," said Dr. Mike Ryan, executive director of WHO's emergencies program. "There is no evidence from randomized control trials that it works, and clinicians have also been cautioned to look out for side effects of the drug to ensure that we do no harm."

Ryan also said it appears not all people who recover from the coronavirus have the antibodies to fight a second infection, raising questions as to whether or not patients develop immunity after surviving Covid-19.

"With regards to recovery and then reinfection, I believe we do not have the answers to that. That is an unknown," Ryan said.