Rodrigo Duterte has been sworn in as president of the Philippines, after a landslide election victory in May.
The controversial former mayor of Davao City, 71, overthrew the political establishment at the polls, promising a "bloody war" on crime and corruption.
In his inaugural speech he promised to make sweeping changes to the country's political system.
But in a nod to his critics he also insisted that he "knows the limits" of his power.
Mr Duterte, who has barely left Davao in the south since his election win, took his oath at a small ceremony at the Malacanang Palace in Manila.
Only state media were permitted to cover the event, but it was streamed live online.
He told the audience he would tackle an "erosion of the people's trust" in the leaders, the judiciary and public servants.
He added: "As a lawyer and a former prosecutor, I know the limits of the power and authority of the president. I know what is legal and what is not."
"I know that there are those who do not approve of my methods of fighting criminality. They say that my methods are unorthodox and verge on the illegal.
"My adherence to due process and the rule of law is uncompromising. You mind your work and I will mind mine."
He also promised to honour international treaties and respect peace deals agreed with rebels at home.
'Change is coming'
The new vice-president, Leni Robredo, was sworn in at a separate ceremony in Quezon City, in the suburbs of the capital.
Both will both serve a single six-year term.
Outside the Malacanang, thousands of people from a left-wing activist group banded together to cheer for Duterte.
"Change is indeed coming," Sevilla Sayco, a 61-year-old rice farmer told Reuters.
"We are happy because the previous administration paid us no attention. But Duterte is pro-poor."
'A leap into the unknown': Jonah Fisher, BBC News
Rodrigo Duterte revels in his reputation as an outsider and a political maverick .
During 22 years as mayor of Davao, he built a reputation for blunt speaking and for supporting the extrajudicial killing of suspected criminals.
Crime rates fell dramatically but human rights groups estimate that more than 1,000 people were killed with no legal process. Many were executed by shadowy death squads.
Mr Duterte's election campaign was littered with obscenities and populist promises but light on details.
So the country must now wait to see how he delivers on pledges to end corruption, restore the death penalty, and shift to a more federal system of government.
On the international front, despite his having bombastically promised to drive a jet-ski to a contested island in the South China Sea, relations between the Philippines and China could be about to improve.
Mr Duterte has indicated that despite differences, and an upcoming ruling from the Permanent Court of Arbitration, he is ready for a more pragmatic, development-focused relationship with the Chinese.
After a period of stability under Benigno Aquino, the presidency of Rodrigo Duterte marks a leap into the unknown.
The two swearing-in ceremonies were being held separately for the first time in the Philippines, which local media attributed to Mr Duterte's decision to a opt for a relatively small event.
But there is a notable political and personality gulf between the two leaders.
Ms Robredo, an anti-poverty campaigner and human rights lawyer, was sworn in by the chairman of the poorest ward of a district in her province, as well as the chairman of the ward in which her new office is located.
Ms Robredo is from the same Liberal Party as outgoing President Benigno Aquino III, who oversaw big improvements in economic growth and foreign investment.
He had less success tackling endemic corruption and inequality, something Mr Duterte has promised to change.