The world has a "long, long way to go" to bring the coronavirus pandemic under control, despite tentative steps in many countries to begin restarting normal life, the World Health Organization's (WHO) top emergencies expert warned on Wednesday.

Dr. Mike Ryan said risks from COVID-19, the respiratory illness caused by the novel coronavirus, remained high at "national, regional and global levels".

"What we all fear is a vicious cycle of public health and economic disasters if lockdowns are eased without the ability to detect fresh outbreaks," Ryan, the head of the WHO's emergencies program, told an online news briefing.

He added that "very significant control" of the virus was required in order to lower the current risk assessment.

Governments around the world are struggling with the question of how to reopen their economies while still containing the virus, which has infected 4.29 million people, according to a Reuters tally, and led to 291,375 deaths.

The European Union pushed on Wednesday for a gradual reopening of borders within the bloc shut by the pandemic, saying it was not too late to salvage some of the summer tourist season while keeping people safe.

But public health experts say extreme caution is needed to avoid new outbreaks.

"We need to get into the mindset that it is going to take some time to come out of this pandemic," Maria van Kerkhove, a WHO epidemiologist, told the same online briefing.