Filipinos went to the polls on Monday in elections that are expected to strengthen President Rodrigo Duterte's grip on power, opening the way for him to deliver on pledges to restore the death penalty and rewrite the constitution. More than 18,000 positions are up for grabs, including half of the seats in the Senate, which has been an obstacle for some of Mr Duterte's most controversial policies. The president is known internationally for his foul-mouthed tirades and deadly drug war, but remains hugely popular among Filipinos fed up with the country's general dysfunction and the leaders who failed to fix it. Mr Duterte wants to bring back capital punishment for drug-related crimes. His narcotics crackdown has led to thousands of alleged pushers and users being killed by police. His tough-on-crime platform – which also includes lowering the age of criminal responsibility from 15 to 12 – was central to his landslide election victory in 2016. People crowded voting centres in the capital Manila even ahead of polls opening at 6.00am local time. About 61 million people are registered to vote. "I voted for many of the candidates endorsed by President Rodrigo Duterte because his government is doing its job," said Myrna Cruz, 51. "I support their programmes, including the anti-drug campaign... but I wish the bloodshed would stop," she adding, echoing many Filipinos' nuanced backing of the crackdown. The opening of the polls was accompanied by isolated outbursts of violence, which is not unusual in the Philippines' frequently bloody elections. At least 20 people were killed and 24 wounded in election-related violence in the run-up to the vote, according to an official count. Early on Monday, nine people were shot and wounded during a confrontation at a polling station on the southern island of Jolo, which is home to insurgents and powerful local clans. The violence is more frequent in the lower-level races and will probably not be a major feature in the contest for the Senate. Winning a Senate majority, something that independent national surveys indicate is well within reach, would give Mr Duterte legislative backing for his anti-crime proposals and his plan to rewrite the constitution. Historically, the nation's 24 senators – who serve six-year terms – have a reputation for being more independent-minded than the lower house. The opposition said a Duterte win in the Senate could lead to the single-term limit for the presidency being lifted, allowing him to seek re-election despite his repeated statements that he would stand down at the end of his mandate. It would also allow him to expand his anti-drug crackdown by bringing back the death penalty, a pledge that the UN Human Rights Council said gave it "deep alarm". The Philippines outlawed capital punishment in 1987, reinstated it six years later and then abolished it again in 2006. Mr Duterte, 74, hit the campaign trail to get his supporters into the Senate, giving two-hour speeches at late-night rallies and routinely insulting their opponents – referring to one by a homophobic slur and accusing another of working for communist guerrillas. The results for municipal and city mayors and councils are expected within hours of polls closing at 6.00pm on Monday, with winners for the Senate and congressional seats likely to be declared from Friday. Even if the presidential term limit is not lifted, the Duterte family looks well-placed to continue its reign. The president's daughter Sara – being viewed by some as the president's potential successor in the 2022 vote – is running to keep her post as mayor in its southern bailiwick of Davao City. Her younger brother Sebastian is seeking, unopposed, the city's vice-mayoral seat, while Mr Duterte's eldest son Paolo is standing for a seat in the House of Representatives.