Be it "DU30" car plates or "The Punisher" T-shirts, Filipinos have been snapping up any merchandise they can featuring President-elect Rodrigo Duterte.

Happy vendors along one highway in Davao, where Duterte is a hero after his tough measures as mayor turned around a town once fraught with drugs and gangs, have been refilling their stalls with stickers, mugs and all things Duterte.

"To Mr Duterte: 'Thank you very, very much. Because of you our business is booming and it has been a big help to our family'," said Lovella Quino, a shop vendor who was selling Duterte mugs, stickers and plates.

Car licence plates bearing Duterte's online abbreviation, "DU30", priced at 150 pesos ($3.25), have been the most in demand item since the firebrand mayor, nicknamed "the punisher" for his measures to tackle crime, won the presidency last week.

"We went here early because we're afraid it will all be sold out," Saudi Lampuni, a tourist looking for car plates, told Reuters.

Vincent Cartilla, another tourist who voted for Duterte, said he was picking up some gifts.

"We want to give these away as presents to our friends who were campaigning for Duterte. These will help relieve their stress and make them feel even better," he said.

A supporter of Rodrigo Duterte wears a "Duterte Shirt" while taking a selfie photograph with other supporters at a life-sized cutout of Duterte inside a restaurant in Davao city.

While Duterte's stand against crime, including advocating extra-judicial killings, has dominated headlines, investors are optimistic he will continue the Philippines' pro-business economic policies that are good for markets.

A printing shop in Davao that has been churning out "The Punisher" shirts, said it was already seeing the benefits of a Duterte presidency on its balance sheet.

Kier Carbonell, owner of Paintline Shirt Printing Services, said there had been many inquiries about their products, including a range called "Victory", showing Duterte as president.

The shirts, similar to a biker gang design to fit the mayor's tough-guy image, are priced between 200 and 400 pesos ($4.3-$8.6) with dealers keen to export the brand outside of Davao.

"We used good quality and design on his T-shirts, so it can be used even after the elections. We are also thinking of continuing this signature design because of his performance and popularity, because people like him," Carbonell told Reuters.

Shop owners said they were expecting demand to spike yet further when Duterte is sworn into office on June 30.