The UK government had announced last week that it would be willing to take a 25 per cent stake in any takeover of the Indian steel major's UK units up for sale.
"There is no guarantee of success. While I want to do everything we can to secure the future, not only for Port Talbot but also for Scunthorpe and steelmaking in Britain, we're coping with a massive oversupply, a collapse in prices from China," Cameron told the House of Commons.
Cameron was joined by Wales Secretary Alun Cairns for a tour of the plant, which employs more than 4,000 workers.
"The Prime Minister underlined our commitment to working with Tata to support the future of steel-making," a Downing Street spokesperson told reporters after the visit.
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Cameron held talks withworkers in the Port Talbot blast furnace control room and finishing lines before holding round-table discussions with unions and managers, including the chief executive of Tata Steel Europe, Hans Fischer.
UK business secretary Sajid Javid is to be questioned by MPs on the steel industry crisis during a Business Select Committee meeting in the Commons tomorrow.
Bimlendra Jha, Tata Steel chief executive, Gareth Stace of trade group UK Steel, and Rickhuss will also appear before the committee.
Other witnesses will include Marc Meyohas of Greybull Capital, which is buying Tata's plant in Scunthorpe.
Tata Steel has said it wants to find a buyer for the entire business, but if no viable bids emerge, it could also be broken up.