The company behind a new UK nuclear power station says “no formal decision” has been made over its future following a report construction would be halted.
The Nikkei Asian Review reported Hitachi’s board would be likely to decide to suspend all work on the Wylfa Newydd plant on Anglesey next week.
In December, the firm said it would do its utmost to ensure the £20bn nuclear power facility went ahead.
A statement from the Welsh Government described the report as “worrying”.
“This is a major project with significant economic benefits to Wales and rest of the country,” the statement said.
“We will continue to monitor the situation very carefully and press the UK government to do everything it can to help bring this project to Anglesey.”
Speculation has been mounting that Hitachi will scrap the Horizon nuclear power plant project due to potential increases in construction costs.
The UK government had been in formal negotiations with Hitachi over the project since June.
The British and Japanese prime ministers met on Thursday but they did not discuss the latest on the nuclear power plant.
Japan’s Shinzo Abe said: “On the Horizon nuclear power plant project, this is a project which is of strategic importance for both nations.
“I do understand that stakeholders including Hitachi are currently discussing this matter and I will wait until they come to a conclusion.
“We did not touch upon this issue in our summit meeting today.”
Theresa May added: “This is a commercial decision for the company, we have been working with them, but it will be a commercial decision for the company.”
Speaking on Friday, Wales’ former first minister, Carwyn Jones, said he found the developments worrying.
“What is troubling me this morning, having heard that news, is this is a case of the UK government being so focussed on Brexit that they are not focused on other issues,” he said.
“And there are bread and butter issues that are hugely important for people living on Anglesey.”
But his successor, Mark Drakeford said that while the situation was worrying, “it’s still speculation”.
Anglesey’s Welsh Assembly member Rhun ap Iorwerth said Hitachi appeared to be “closer to a decision on Wylfa not progressing”.
“The signs aren’t looking good,” he told BBC Wales’ Good Morning Wales.
On Friday, the firm said suspension of the project remained an option.
“No formal decision has been made in this regard currently, while Hitachi has been assessing the Horizon project including its potential suspension and related financial impacts in terms of economic rationality as a private company,” it said in a statement.
The new nuclear plant would aim to have a generating capacity of 2900 MW by the mid 2020s and have a 60-year operational life.
Shares in the Japanese company jumped 8% after the report the project would be suspended.
A spokesman for UK government’s Department for Business, Energy and Industrial Strategy, said: “Negotiations with Hitachi on agreeing a deal that provides value for money for consumers and taxpayers on the Wylfa project are ongoing.
“They are commercially sensitive and we do not comment on speculation.”
The original Wylfa nuclear plant near Cemaes closed in 2015 after more than 40 years’ service.