South Wales is heading for an economic shock on the same scale as Thatcher-era deindustrialisation as Tata prepares to close the blast furnaces at its Port Talbot steelworks, a shadow cabinet minister has warned.

Jo Stevens, the shadow Wales secretary, said the fallout from the company’s decision to close the blast furnaces would be felt for decades as it was in the 1980s, as she pushed ministers to do more to help workers facing redundancy.

Tata announced this year it planned to close both blast furnaces while it builds a new, less polluting electric furnace – a decision that will cost up to 2,800 jobs directly. Labour has urged the company to delay a final decision on redundancies, promising the company a share of its £3bn clean steel scheme if it wins the next general election.

Speaking to the Guardian at the steelworks, Stevens said: “If these jobs are lost, Port Talbot probably loses its identity. There’s a very proud history of steelmaking here … and the danger is that there is nothing here to replace it.”

Stevens grew up close to Shotton in north Wales, where 6,500 people lost their jobs overnight after British Steel closed the steel making plant there in 1980, in what was the biggest single redundancy on a single day in western Europe.

“I saw what happened in my community,” she said. “I was 14 years old at the time, and it took us decades to recover from it. Pretty much every child in my school had family in the steelworks, and I’m really worried that the same thing is going to happen here.”

Tata announced in January it would close down its two blast furnaces while it builds a new electric arc furnace at the site. The decision is set to lead to the loss of most of the company’s 4,000-strong workforce at Port Talbot, though it says that when it reopens three years later it will still employ hundreds of people.

Tata says the plant is losing £1m a day, and is consulting unions over how to make the necessary redundancies.

Labour hopes it might delay that process until the election, and is promising to support the company with a share of its £3bn clean steel fund. Stephen Kinnock, the local Labour MP, has previously promised that “the cavalry is coming in the form of a Labour government.”

However, both Stevens and company employees say they are concerned the company’s decision last week to close the coal processing ovens earlier than expected could accelerate the closure of the entire plant.

Stevens said: “There is anxiety that it might accelerate to the closure of the blast furnaces.”

Mark Davies, who works at the steelworks, added: “If you can’t source the raw materials, that will bring the issue of the furnace forward.” Barrie Evans, another steelworker, said: “We are going to find it hard to source the materials we need. There is a fear it could all come crashing down quite suddenly.”

With thousands of people facing redundancy, the government has launched a £100m Port Talbot transition board to support employees, businesses and local communities affected by the steelworks’ closure. However, while the board has met a handful of times, the government says it does not plan to use any of its money until the company has confirmed its redundancy plans.

The Guardian has seen correspondence from government officials asking large employers in the area if they have any jobs available for those who are soon to find themselves out of work. In a sign of how difficult the transition is likely to be, however, one of the biggest companies in the region has replied that is has jobs going 150 miles (240km) away in north Wales, but only a “small” number in nearby Newport.

Stevens said the government should start allocating the money from the transition fund immediately to prevent further economic damage. “We’ve heard nothing about what that plans to do, how it proposes to help people affected by this if these jobs do go,” she said.

“You can’t wait until the end of the year and then go: ‘Right, OK. We’re going to think about starting to work on this now.’ There’s got to be some preparation.”

David TC Davies, the Wales secretary, said: “It’s always been known that the £100m will be invested directly in skills, training and job creation as soon as the outcome of the ongoing consultation between Tata and its workforce is known and it is understood exactly which workers are affected.”

He added: “It’s a great shame that Ms Stevens is highly critical of this vital initiative which will help find alternative employment for those impacted.”