BEIRUT, Lebanon — Protesters returned to downtown Beirut on Sunday to demand that the government resign over its inability to remove enormous heaps of garbage from the city’s streets. Demonstrations on Saturday led to clashes with the police, who used water cannons, tear gas and rubber bullets to disperse the crowds. Dozens of people were injured.

The garbage crisis has become the most glaring sign — at least to the senses of sight and smell — of the political paralysis that grips the nation and has unified many Lebanese, usually divided by sect, religion and region, in what the protesters call the “you stink” campaign.

The office of president has been vacant for more than a year, and Parliament essentially re-elected itself after being unable to agree on new elections, even as the country absorbed more than 1.2 million refugees from the Syrian civil war.

By Sunday evening, thousands of people had gathered outside the Grand Serail, the stately Ottoman-era building where Prime Minister Tammam Salam has his office. Water hoses and tear gas guns were again turned on protesters after stones were thrown at the police. Organizers of the campaign said that the men throwing the stones, whose faces were covered, did not represent the movement.

Fouad al Hassan, an actor known for his work in television comedies, said he took part in the protests because “I want to change the system.”

“We want new blood or the country will stay the same,” added Mr. Hassan, 65. “Today, it’s too late for me, but I want it for my children. I want them to live a better life.”

Aline Shirfan, a 21-year-old civil engineer, said it was her first time participating in a demonstration: “I have nothing to lose, I’m so desperate. If we don’t die from a bullet we will die from cancer from the trash smell.”

The Red Cross reported that at least 20 people were hurt in the violence on Sunday.

Later, the crowds moved toward Martyrs Square, the site of huge rallies after the car-bomb assassination of a former prime minister, Rafik Hariri, in Beirut in 2005. Those rallies eventually led to the withdrawal of Syrian troops and ended de facto Syrian control of the country, though Syria and the militant group Hezbollah, its Lebanese ally, denied any involvement in Mr. Hariri’s assassination.

Mr. Salam admitted at a news conference that “excessive force” had been used on Saturday, and that the demonstrators had a legitimate grievance.

“What happened yesterday was the result of accumulating matters that have been building up and increasing the people’s suffering as the result of the vacuum we are living,” Mr. Salam said. He promised that he would hold government officials accountable and said, “I won’t cover anyone.”

Asked if he would resign, Mr. Salam said, “My patience is limited, and it’s linked to yours.”

For many years, Beirut’s trash and that much of central Lebanon was sent to a landfill near Naimeh, a town south of the capital.

But the amount of trash long ago exceeded that landfill’s capacity, and communities nearby complained of the smell and blamed it for health problems. Protesters blocked the road to the landfill last summer, causing a pileup of garbage in Beirut then.

They relented after the government promised to find alternatives. But when no alternatives materialized, the protesters blocked the road again last month, leading to the present crisis.

The complaints that brought ordinary citizens into the streets of Beirut over the weekend were not unlike the festering anger that prompted recent protests in Baghdad over the Iraqi government’s failure to provide enough electricity to power air-conditioners when temperatures soared well above 100 degrees Fahrenheit. In other countries, like Brazil, Honduras and Guatemala, leaderless protests have arisen suddenly and more or less spontaneously over allegations of government corruption and widespread perceptions of a lack of accountability.

On Sunday, some Lebanese who did not take part in the demonstrations expressed strong support for them. “Unfortunately, today is my shift so I can’t join. All my friends are already there,” said a woman who was working at a market and identified herself by her first name, Hiba. “This country is not functioning.”

As she was speaking, the electricity in the store went off. “Now you know what I mean,” she said.