"It is with gratitude and humility and with a great sense of responsibility that I present myself today," Guterres said in his first comments after being acclaimed by the assembly.

The 193 member states of the United Nations had gathered to ratify the Security Council's decision - also by acclamation - to choose Guterres to head the organisation.

The former prime minister of Portugal, who served as UN High Commissioner for Refugees for 10 years to December, is from 1 January to be the ninth secretary-general, with a five year term. He succeeds Ban Ki-moon, a South Korean.

Speaking in Lisbon, Portugal's president, Marcelo Rebelo de Sousa, welcomed the choice of Guterres as UN chief as "a great joy" and "a unique event in the life of the country".