Voters streamed into a polling station in Portsmouth, a city nestled along England’s southern coast that is known for its naval base and historic dockyard, on Thursday morning as ballot workers greeted them warmly.

Older couples walked hand in hand into the local church, which had been temporarily fitted out with ballot boxes, alongside parents with children in strollers, and young adults rushing in on the way to work.

One by one, they weighed in on the future of the nation in a vote that polls suggested could end 14 years of Conservative-led government.

“I just want to see change,” said Sam Argha, 36, who was outside the polling station on Thursday morning. “I just really want to see us do something differently.”

Many people in the city expressed a similar desire for a new start at a moment of intense national uncertainty. Polls have predicted that the election could be a major turning point, with the center-left Labour Party expected to unseat the right-wing Conservative Party, possibly with a crushing landslide.

Portsmouth North is considered a bellwether seat — the area has voted for the winning political party in every general election since 1974.

It also serves as a microcosm of the broader national challenge facing the governing party: a longstanding Conservative constituency held by a popular candidate that is now at risk of being lost, and a largely disillusioned electorate that expressed frustrations with their quality of life and what many see as a lack of leadership.

The seat has been held since 2010 by Penny Mordaunt, a Conservative lawmaker whose prominent role at the coronation of King Charles III last year, when she wielded a heavy, jewel encrusted ceremonial sword, drew international attention to her steadiness and poise.

Ms. Mordaunt, who is seen as a possible contender for her party’s leadership, is widely liked in Portsmouth, and some locals said they had no intention of heading in a new direction. But polls have suggested that Labour voters in the constituency could still overtake Conservative support in Thursday’s vote.

The centrist Liberal Democrats — considered the third most popular party here — and the hard-right Reform U.K. party could also siphon off votes from the Conservatives.

“My hopes are for a much more compassionate government from Friday,” said Grahame Milner, 62, who was walking in the city center with his husband of three decades on Wednesday afternoon.

Many of the shops surrounding the couple were vacant or boarded up. Graffiti marked the sides of shuttered department stores. There is little to attract people to the area, other than the bookmakers, charity shops and small stores selling vapes, Mr. Milner said.

He first came here to serve in the Navy — the city is home to the country’s biggest naval base — and was deployed during the 1980s Falklands War as a chef aboard a military vessel. He was pushed out of the military because of his sexual orientation, he said, and later became deeply involved in union work after returning to civilian life. He had already cast his ballot by postal vote last week.

“The austerity program has been absolutely crippling to working-class people,” Mr. Milner said, pointing to the number of working people relying on food banks just to get by. “This is just not the Britain that I served in the military for.”

Concerns about the hollowing-out of the National Health Service, a cost-of-living crisis that has left many struggling, debates about immigration, and the fallout from Britain’s withdrawal from Europe were front of mind for many locals.

Some said they had no plans to vote at all, disillusioned by politicians from across the spectrum.

“It’s always been Labour for us, but I am not voting this year,” said Tracy Patton, 59, who has lived in the city all her life and said she was fed up with politics. She sat outside a cafe on Wednesday evening, reminiscing with friends about how the once busy marketplace had changed.

“It was bustling, there was atmosphere,” she said. “But now, it’s going through decline. There is just no money in England anymore.”

For some younger voters, the prospect of an uncertain future has weighed heavy. Daisy Quelch, 28, and Kiran Kaur, 24, were packing up after an outdoor boxing class near the waterfront on Southsea Common.

“Sometimes it feels like our world is crumbling,” Ms. Quelch said, adding that she was particularly worried about climate change and the environment. “We want to see changes, but it can’t happen quickly enough.”

Earlier this year, residents were warned not to swim in the sea as the local water company had released raw sewage along the coastline, contaminating the water.

Water pollution has become a campaign issue in many parts of Britain, as some blame the government for its inability to stop the water industry — which was privatized during the Conservative government of Margaret Thatcher in the 1980s — from releasing untreated waste into the waterways.

Some formerly stalwart Conservative supporters said they were rethinking their vote. Several were considering casting their ballots for Reform U.K., the populist anti-immigration party led by Nigel Farage, a brash and polarizing figure who has shaken up the general election campaign.

But others defended the Conservative Party. In Dixie’s Pub just off the high street, a group of patrons played pool on the eve of the election, the clack of billiard balls mingling with chatter.

Andrew Revis, 57, was enjoying a pint at the bar after finishing work at his nearby accountancy office, and said he felt that the Conservatives and Ms. Mordaunt, who he described as a capable and committed lawmaker, were receiving undue criticism.

“They are getting a lot of stick, but I don’t think it’s entirely been in their control,” he said, pointing to the devastating impact of the coronavirus pandemic and the war in Ukraine that created unexpected hardship.

“It’s the cost of living,” said Kerry Harris, 36, who sat outside the Iceland supermarket with her niece Shanice Bakes, 19, on Wednesday evening. She gestured to their bags. There was a time, Ms. Harris said, when a full shopping cart of groceries would cost about 50 pounds, or $65, but now she couldn’t fill one bag for that price.

“And they don’t put your wages up, do they?” she added.