He was addressing a gathering of European leaders of the centre right.
German Chancellor Angela Merkel said it would take years to overcome the crisis but "we need to have more Europe".
The key proposal on the agenda of the gathering in the Belgian capital later on Thursday is how to enforce budgetary discipline with automatic penalties for those eurozone nations that overspend.
Germany and France are pushing for new European Union treaties, saying stricter fiscal rules should be enshrined there.
Mr Sarkozy said Europe was in much danger.
"Never has Europe been so necessary. Never has it been in so much danger," he said.