“If I send my marines to drive away the Chinese fishermen, I guarantee you not one of them will come home alive,” Mr. Duterte said.

Philippine President Rodrigo Duterte said Monday there was no way to stop Chinese nationals from fishing in his country’s exclusive economic zone claimed by China and added that he would not risk losing Filipino forces in a clash with the Asian superpower in the disputed South China Sea.

“When Xi says I will fish, who can prevent him?” Mr. Duterte said as he defended his nonconfrontational approach to China over the territorial disputes in his annual state of the nation address before a joint session of Congress. He was referring to Chinese President Xi Jinping.

“If I send my marines to drive away the Chinese fishermen, I guarantee you not one of them will come home alive,” Mr. Duterte said, adding that diplomatic talks with Beijing have allowed the return of Filipinos to disputed fishing grounds where Chinese forces previously shooed them away.

Critics have repeatedly criticised Mr. Duterte, who has nurtured friendly ties with Beijing, for not standing up to China’s aggressive behavior in the disputed waters and deciding not to immediately seek Chinese compliance with an international arbitration ruling that invalidated Beijing historic claims to virtually the entire sea.

On his battle against illegal drugs and corruption, Mr. Duterte asked Congress to allow the reimposition of the death penalty for drug-related heinous crimes and economic plunder. He said the drug menace, which he called a “social monster,” could not be crushed unless corruption is eliminated.

The Philippines’ long-simmering territorial rifts with China and Mr. Duterte’s centerpiece campaign against illegal drugs and corruption were spotlighted in his speech. But he also asked for Congress’s help in dealing with diverse social ills and governance issues ranging from slow internet, delays in releases of government clearances to traffic jams.

Mr. Duterte outlined problems he had resolved, sometimes through scare tactics, like the easing of a water shortage last summer in the Philippine capital after he threatened to fire officials.

Although the annual speech is traditionally replete in protocol and formality, he injected sexual jokes, curses and threats that have been the trademark of his often-rambling speeches. During the water crisis in the capital, for example, he said he did not want to travel to Manila. “What if my girlfriend will not be able to take a bath, she will smell like hell,” he said.

When he asked Congress to pass new tax reforms that would further raise excise taxes on tobacco and alcohol, Duterte asked if there were smokers in the audience, which included foreign diplomats. “Who smokes here? They should be exterminated from the face of the earth.”

Mr. Duterte (74), took office in June 2016 and has remained hugely popular in opinion polling despite drug war deaths that have sparked international alarm and other controversial policies.

More of his allies captured congressional seats in midterm elections in May, giving them a tighter grip on the legislature, especially in the 24-member Senate, which opposed some of his key legislative proposals last year, including reinstating the death penalty and amending the pro-democracy constitution.

More than 5,200 protesters rallied despite a downpour outside the House complex to call for Duterte’s removal while a smaller number of pro-Duterte supporters rallied separately. Left-wing protesters burned a mock Chinese flag and a giant mural with the images of Duterte, Chinese President Xi Jinping and President Donald Trump.

Military and police were placed on full alert and authorities declared a no-fly zone over the venue and outlying areas to ensure security.

“We have had enough of this government’s ‘kill, kill, kill’ policy,” Danilo Ramos, a left-wing leader of a farmers’ group, said. “The Duterte presidency is killing its constituents in so many ways.”