Europe must have 'firm' response to Trump: Hollande

French President Francois Hollande on Saturday urged Europe to form a united front and provide a "firm" response to his US counterpart Donald Trump's controversial policies.

"When there are statements from the US president about Europe and when he talks about Brexit being a model for other countries, I think we must respond," Hollande told reporters the sidelines of a summit of southern EU nations in Lisbon.

He was speaking a day after Trump called Britain's decision to exit the European Union as a "wonderful thing" during a joint news conference in Washington with visiting British Prime Minister Theresa May.

"When he adopts protectionist measures, which could destabilise economies not just in Europe but the economies of the main countries of the world, we have to respond," Hollande added.

"And when he refuses the arrival of refugees, while Europe has done its duty, we have to respond.

"We must affirm our positions and then engage in a firm dialogue on what we think", with a goal towards solving global problems, the French president said.

Trump is due to speak Saturday with Hollande, as well as German Chancellor Angela Merkel and Russian President Vladimir Putin who he has repeatedly praised.

The US president has rattled America's traditional European allies with a range of radical policy plans.

Trump has called NATO "obsolete", announced he would rip up a planned transatlantic trade plan and supported Britain's move to leave the EU, praising the decision during Friday's meeting with British Prime Minister Theresa May.

On Friday he also signed a sweeping executive order to suspend the arrival of refugees and impose tough controls on travellers from seven Muslim countries.

"The talk which we hear coming from the United States encourages populism and extremism," Hollande said.

"We have to be conscious of the responsibility we have... Europe is a force, Europe is a guarantee, Europe is protection, and Europe is also a space for liberty and democracy," the French president said.