The UK’s manufacturing sector has suffered a double blow after Liberty Steel and the rolling stock manufacturer Hitachi announced job cuts affecting up to 505 staff across the UK.

The twin announcements prompted criticism of the government’s industrial strategy from Labour and trade unions.

Liberty, owned by the UK-based steel magnate Sanjeev Gupta, said it was proposing to cut operations in South Yorkshire and south Wales in response to “challenging market conditions”. Up to 355 jobs are at risk, although the firm will offer affected staff jobs elsewhere in the company.

Labour said the cuts should spur the government into action to save the floundering UK steel sector, amid ongoing uncertainty about the future of Scunthorpe-based British Steel.

“This is devastating for those who have lost their jobs at Liberty Steel in south Wales and South Yorkshire,” said the shadow steel minister, Gill Furniss.

“The UK steel industry has faced countless challenges, and under the Tory government they have received little to no help.

“The time for excuses is over. The prime minister must act now to save the UK steel sector and prevent further job losses,” she said.

“Labour promised in its manifesto to protect the long-term future of our steel sector by ensuring public procurement, tackling industrial energy prices, investing in research and development and upgrading existing production sites.”

Hours after Liberty’s proposals emerged, Japanese-owned Hitachi Rail announced plans to “resize” the workforce at its Newton Aycliffe rolling stock assembly plant in Country Durham, with up to 250 jobs at risk.

It said the decision had nothing to do with Brexit and was instead about a transition to a new operational model that would also see it invest £8.5m. Hitachi said it would seek to redeploy as many staff as possible, rather than making them redundant.

The trade union Unite’s regional officer Pat McCourt said government policy on buying trains for the UK’s rail network was to blame.

“These redundancies need to be laid at the door of the government. Its existing procurement policies mean that major contracts for new trains are too readily awarded to overseas companies, depriving factories in the UK of work.”

The government said both announcements were commercial decisions for the companies.

On Liberty, a spokesperson added: “We remain dedicated to maintaining a stable and thriving future for the UK steel industry.

“We are monitoring the situation closely and are in contact with Liberty and the unions, who are undertaking this consultation.”