Iron and steelmaking operations at a huge steel plant are to be "paused" because of issues with the supply of raw materials and services.
SSI said preparations are being made to systematically reduce production at the site on Teesside during the course of today.
The Thai-owned firm said it would retain the plant in a condition whereby it can be brought back into production "at an appropriate point".
The coke ovens and power station on the site in Redcar will continue to operate at a reduced level, but production at the south bank coke ovens will cease and the plant mothballed.
Around 2,000 workers are employed on the site, which was bought by SSI from Tata Steel.
Cornelius Louwrens, SSI's UK business director and chief operating officer said: "It is with great regret that we have had to make this announcement and we are deeply aware of the concern it will give to our employees and their families.
"The problems within the global steel industry have been well publicised in recent weeks and our decision follows a major deterioration in steel prices affecting our business during the course of this year.
"Our parent company and other stakeholders have given great support to the business, and the decision to pause our iron and steel production has been taken reluctantly and in a scenario where no other practical options are available at present.
"We are taking this pause in production in order to re-evaluate and assess the situation following the outcome of ongoing discussions with our various stakeholders, including Government and suppliers.
"Discussions will be held as soon as possible with our trade unions and employee representatives to clarify the effect the production pause will have on our employees "
The Government announced that a top-level steel summit is to be held urgently, amid warnings the UK industry was at "breaking point".
A debate on the plight of the industry was held in the Commons on Thursday, when MPs warned about its "dire prospects".
Business Minister Anna Soubry said officials from the Welsh Assembly and Scottish Parliament would be invited to join their Westminster counterparts alongside worker and company representatives.
Ms Soubry told the Commons she echoed Prime Minister David Cameron's pledge for the Government to do everything it could to support the industry.
The minister is planning to visit China next week to discuss issues affecting the industry, although she noted the UK is unable to control global steel prices and over-production.
She said: "I will do all I can to make the argument within Government where it is the case we're doing things we shouldn't do ... because although I'm not an actual free marketeer, I do believe there is a role for Government."