Duterte sworn in as president of Philippines

In this image made from video provided by Radio Television Malacanang, new Philippine President Rodrigo Duterte takes the oath during the inauguration ceremony in Malacanang Palace, June 30, 2016 in Manila, Philippines. (Radio Television Malacanang via AP Video)

MANILA, Philippines - Rodrigo Duterte was sworn in Thursday as president of the Philippines, with some hoping his maverick style will energize the country but others fearing he will undercut one of Asia's liveliest democracies amid threats to kill criminals en masse.

Minutes later he told the nation that he would wage a "relentless" and "sustained" battle against crime and warned officials that he would not tolerate corruption.

Chinese President Xi Jinping on Thursday sent a congratulatory message to Duterte on his inauguration, saying he is willing to work with Duterte to push for improvement of relations between the two countries, Xinhua reports.

Xi said the good-neighborly relationship between China and the Philippines had lasted around 1,000 years, and was the right direction for the two countries to progress, Foreign Ministry spokesperson Hong Lei said at Thursday's daily press conference.

In an acceptance speech at the president's palace, Duterte said there had been an erosion of trust in the country's leaders and people were hungry for change.

The 71-year-old former prosecutor and longtime mayor of southern Davao city won a resounding victory in May's elections in his first foray into national politics.

Duterte, who begins a six-year term as president, captured attention with promises to cleanse the poor Southeast Asian nation of criminals and government crooks within six months — an audacious pledge that was welcomed by many crime-weary Filipinos but alarmed human rights watchdogs and the influential Roman Catholic church.

Shortly after Duterte's election win, policemen launched an anti-drug crackdown under his name, leaving dozens of mostly poor drug-dealing suspects dead in gunfights with police or in mysterious circumstances.

Days before his swearing in, Duterte was threatening criminals with death if they wouldn't reform.

"If you destroy my country, I will kill you," he said in a warning to criminals in a speech during the last flag-raising ceremony he presided as mayor in Davao city this week.

Philippine Vice President Leni Robredo, second right, is sworn in by village chiefs Ronaldo Coner and Regina Celeste during inauguration ceremonies in suburban Quezon city, north of Manila, Philippines June 30, 2016. (AP Photo / Aaron F avila)

Vice President Leni Robredo, a human rights lawyer who comes from a rival political party, was sworn in earlier in a separate ceremony. Vice-presidents are separately elected in the Philippines, and in a sign of Duterte's go-it-alone style, he has not met her since the May 9 vote.

In a country long ruled by wealthy political clans, Duterte rose from middle-class roots. He built a reputation on the campaign trail with profanity-laced speeches, sex jokes and curses that sideswiped even the widely revered pope and the United Nations.

His brash style has been likened to that of presumptive US Republican presidential nominee Donald Trump, although he detests the comparison and says the American billionaire is a bigot and he's not.

Duterte is the first president to come from the country's volatile south, homeland of minority Muslims and scene of a decades-long Muslim separatist insurgency, where he said his central Philippine-based family migrated in search of better opportunities.