French centrist candidate Emmanuel Macron and far-right leader Marine Le Pen are hoping to bring in big crowds at competing rallies in Paris as the unpredictable presidential race nears its finish.

Meanwhile, far-left candidate Jean-Luc Melenchon, enjoying a late poll surge, is campaigning on a barge Monday floating through Paris canals. And conservative Francois Fillon is taking his tough-on-security campaign to Nice, scarred by a deadly truck attack last year.

The race is being watched internationally as an important gauge of populist sentiment, and the outcome is increasingly uncertain just six days before the April 23 first round.

The top two vote-getters advance to the May 7 second round, and polls now suggest that Le Pen, Macron, Melenchon and Fillon all have a chance of reaching the runoff.