SYDNEY — Angry mobs swarmed Australia’s second-most-populous city, Melbourne, for a second straight day on Tuesday, after officials halted all nonessential building work in the city following a violent demonstration against vaccine mandates for the construction industry a day earlier.

Australia has been grappling with an outbreak of the coronavirus’s highly contagious delta variant since mid-June, with Melbourne, Sydney and the capital Canberra in strict lockdowns for weeks.

As frustrations grow over the long shutdowns, labor unions and some lawmakers have blamed right-wing activists for infiltrating the ranks of construction workers, fomenting trouble and spreading misinformation about vaccines ahead of a state government requirement that all construction workers have at least one vaccine dose by the end of this week to help curb the virus’s spread.

“There is a very small group of people, not just in Melbourne but around the country, hard-right extremists who are trying to weaponize the covid-19 lockdown,” said Bill Shorten, a federal lawmaker with the main opposition Labor Party and a former union leader, describing the people as a “rent-a-crowd” organized by “hard-right man-baby Nazis, just people who just want to cause trouble.”

Encrypted messages circulating on social media encouraged demonstrators to wear “hi-viz” construction gear to blend in, and several prominent far-right identities were spotted at Monday’s rally, according to local media reports.

The latest protests follow a string of recent demonstrations across the country, including one where construction workers blocked streets across Melbourne in a sit-down against the closure of construction site break rooms.

Officials in Melbourne say the frequent movement of construction workers — and in some cases, failures to comply with public health orders — is spreading the coronavirus, leaving them with “no choice” but to pause construction for two weeks while they work with the industry to improve compliance and boost vaccinations.

The government has linked the construction sector to more than 400 cases in the latest outbreak and said during recent inspections that half of all construction sites did not meet coronavirus safety requirements.

Union leaders are broadly supportive of vaccines as a way to keep their industry working, but they have stopped short of endorsing the state government’s vaccine mandate.

Melbourne went through one of the world’s longest lockdowns last year. The city of 5 million was shuttered for almost four months. The latest shutdown is the city’s sixth since the pandemic began, and patience is wearing thin.

Footage on television and social media shows protesters marching through the city’s streets, setting up flares and chanting, with mounted police and officers in riot gear following them. A local television reporter said he and his cameraman were sprayed with what he believed was urine by protesters. Footage shows him being tackled by protesters and later pelted with a soda can in the back of the head during a live broadcast.

International border closures, snap lockdowns and a high rate of compliance with public health orders have made Australia a relative covid success story, with just fewer than 89,000 confirmed cases and 1,178 deaths since the start of the pandemic. However, a slow start to the country’s vaccination program meant it has struggled to suppress outbreaks of the delta variant, leading to fresh lockdowns just as the United States and Europe were enjoying vaccine-related freedoms over the summer.

State border closures designed to keep the coronavirus from spreading to states where the virus has been stamped out have also upended domestic travel and stranded scores of Australians internally.

Most of the restrictions in Victoria, New South Wales and Canberra will likely remain in place until at least 70 percent of the population age 16 and older are fully vaccinated, which based on the current pace of immunizations could be in late October or early November.

Read more: