The steel industry is like a patient on an operating table and is "likely to die" without urgent help, the Government has been told.
The stark warning was given by Gareth Stace, director of trade body UK Steel during evidence to a committee of MPs.
He said that a fifth of the sector's UK workforce had lost their job or were facing redundancy following a recent wave of cuts.
"If we were a patient on an operating table, we are bleeding very quickly. And we are likely to die on that table," he told the Business Select committee.
Shortly after the MPs started the session, the Business Department issued a statement saying the steel industry will be able to take advantage of "special flexibilities" to comply with new EU rules on emissions.
Business Secretary Sajid Javid, who is visiting Brussels tomorrow for talks on steel, said he recognised the costs the regulations could have, so he was working with businesses to agree a "flexible" way forward that does not damage competitiveness.
Mr Stace told the select committee that the emissions directive was the easiest of five measures the industry wanted action on.
Other issues included reducing high energy costs and business rates, tackling unfair trade, and having more local content in orders.
Roy Rickhuss, general secretary of the Community trade union, said the current crisis in the industry seemed to be "out of control".
"We don't seem able to find a solution. We can't say we will change a working practice, or work more flexibly. It is not enough."
Mr Rickhuss revealed that unions had not been invited to take part in working groups set up after a one-day summit earlier this month.
Asked about the impact of the summit, he replied: "It is sad it came to a crisis to make people sit up and take notice. We have been making these points for a long time."
Thousands of job cuts have been announced in recent weeks by Tata Steel and SSI in Redcar, Scunthorpe and Scotland, with cheap imports and high energy costs being blamed.
Further losses are threatened at Steel processing giant Caparo Industries, which has gone into administration.
Steel workers will lobby MPs tomorrow as part of growing demands for Government action to tackle the crisis.
Workers from steel communities in Teesside, Lincolnshire, Yorkshire, the West Midlands and south Wales will travel to Parliament ahead of an opposition day debate on the wave of job losses in the sector.
Unite assistant general secretary Tony Burke said: "The message from steelworkers and their communities to the Government is clear. Step in and support the industry to save our steel before it's too late.
"We have already seen the consequences of the Government's failure to act on Teesside. Instead of intervening to keep the coke ovens burning at Redcar, ministers sat on their hands and allowed a key industrial asset to close forever taking with it the livelihoods of thousands of people.
"The approach by ministers so far has been to deal with the symptoms of the steel crisis, when what steel and manufacturing communities want is action that secures UK steelmaking and secures their futures."
Mr Rickhuss added: "Our message this week remains a loud and clear appeal to the Government to save our steel. We have already seen thousands of jobs go in Redcar, now thousands more are on the line in Scunthorpe, South Yorkshire, Lanarkshire and within Caparo sites across the UK.
"The Government still needs to give a sign to steel producers that this vital foundation industry has a future.
"The eyes of the UK are on the steel industry and people will be watching the response of ministers to the issues raised in Parliament this week. The Government needs to demonstrate that it has heard the steelworkers and employers' concerns and that it understands the urgency of the situation."
Mr Javid said: "Cutting red tape was one of the issues discussed at our recent steel summit and it is important that we are making progress quickly on it. I will also be going to Brussels tomorrow to make the case for firmer action on unfair trade."