Belgium is experiencing a dangerous surge in coronavirus cases after relaxing many of its lockdown measures, health officials said Wednesday, warning of a possible second wave epidemic.

The Belgian national security council will meet on Thursday and could decide to postpone the next phase of the country's staggered return to normal economic and social life.

But already at a public briefing on Wednesday, officials urged residents to take better care to respect social distancing guidelines and to wash their hands more often.

"It is very important that we work together to halt this snowball effect before it provokes a new avalanche," said spokesman Boudewijn Catry.

"The situation is not without an exit, we can still change the course of events, but we must act fast."

Catry was himself replacing Belgium's federal COVID-19 spokesman Yves van Laethem, who he said had gone into voluntary quarantine after being exposed to a coronavirus carrier.

Belgium suffered one of Europe's worst per capita outbreaks of coronavirus earlier this year, but along with its neighbours was able to bring it under control.

Now, however, the number of cases is increasing again. There were 184 new infections per day on average last week, up by 98 percent over the previous seven days.

The majority of new infections are among the active population aged between 20 and 59, Catry said, but nevertheless the hospitalisation of serious cases is also increasing.

"Last week we counted on average 12 new hospitalisations by day on average, up from 9.7 the week before. We expected this increase. This indicator follows that of new infections with a two- to three-week delay."

Some 64,258 cases have been detected in Belgium since the pandemic swept around the world, and 9,805 people have died.