"It's completely off the charts," said Erik Guldager, who owns the gallery that is selling Kurt Westergaard's cartoon.
Westergaard's caricature of the prophet Muhammad wearing a bomb in his turban was one of 12 cartoons published by Danish daily Jyllands-Posten in 2005.
Westergaard on Friday renamed a 2009 cartoon "Je suis Charlie" and pledged to give proceeds from reprints to the French satirical magazine where gunmen on Wednesday killed 12 people.
Within hours Galleri Draupner in the western Danish town of Skanderborg was inundated with orders from around the world for the 50 euro ($59) reprints.
"He wants to support Charlie Hebdo and their contribution to freedom of speech and their right to do their work," Guldager told AFP.
"People from all of Denmark and Europe, and even distant corners of the world now, have logged on and want to support Charlie Hebdo and Kurt Westergaard's drawing for them," he added.
At last count "hundreds" of reprints had been sold but by early afternoon Guldager was unable to check his emails due to the "huge number of orders coming in," he said.
The 79-year-old artist has lived under police protection since his cartoon was published almost a decade ago, sparking massive protests.
In 2010 an axe and knife-wielding man broke into his home, forcing him to take refuge in a panic room with his five-year-old granddaughter.
The renamed painting featured a man standing on a tightrope above a precipice, holding a pen in one hand and the rope in the other. The rope is tied to a sign that says "Free speech".
Guldager said his gallery has had to "withstand a bit of everything" since agreeing to sell Westergaard's work in 2009, but he declined to go into any details for fear of inspiring violent extremists.
"I have been with Kurt around most of the world in the past six years, and it's probably the closest you will get to James Bond [films] in Denmark," he said.
Westergaard declined to comment, citing health reasons.