Costa was speaking to journalists after a visit to the Portugal Fashion show in Lisbon.

“In the first place I should like to express to all the British people, to the British government and, in particular, to the British parliament my solidarity and my condolences at this terrorist attack, which highlights what must be the priorities on which Europe has to concentrate... instead of wasting time... creating conflicts between us," he said, in a reference to comments by the president of the Eurogroup, Jeroen Dijsselbloem, about a lack of financial discipline in southern Europe.

"It's sad that events like these are necessary to remind us that we must unite," Costa said.

He noted that the attack in London took place “precisely a year after the dramatic attack (…) in Brussels and shows well that the terrorist threat is a global threat."

He called for “greater police cooperation, greater judicial cooperation and greater exchange of information” between European countries, as well as “work to prevent ... radicalisation”.

Asked whether any Portuguese nationals were among the injured, Costa said that there was so far no indication of this.

Eye witnesses report that a car mowed down several pedestrians on London's Westminster Bridge before crashing into fencing outside the Houses of Parliament. A man then jumped out of the car brandishing a knife and stabbed a policeman before being shot dead by other police.

According to the latest information from London's Metropolitan Police, at least four people have died so far as a result of the attack, including a police officer and an attacker. Another 20 people were injured, including several police officers.

The authorities are treating the incident as a "terror attack”.