Friday’s cyber-attack has affected more than 200,000 victims in 150 countries, Europol chief Rob Wainwright says.
Speaking to Britain’s ITV, he said the world faced an escalating threat, and there was concern about the level of potential attacks on Monday morning.
The virus took control of users’ files, demanding payments; Russia and the UK were among the worst hit countries.
Security experts have warned that another attack is imminent and could be unstoppable.
Mr Wainwright said he was concerned that the numbers of those affected would continue to rise when people returned to work on Monday morning.
“We’re in the face of an escalating threat, the numbers are going up,” he said, adding that the current attack was unprecedented.
“We are running around 200 global operations against cybercrime each year but we’ve never seen anything like this.
“The latest count is over 200,000 victims in at least 150 countries. Many of those victims will be businesses, including large corporations. The global reach is unprecedented.”
However, Mr Wainwright said that so far “remarkably few” payments had been made by victims of the attack.