Public service broadcasting (PSB) is unlikely to survive without a radical change to regulations, says Ofcom.
The media watchdog suggests streaming services like Netflix might offer PSB content, which could focus on specific viewer groups.
The UK's current public service broadcasters are the BBC, ITV, Channel 4, STV, S4C and Channel 5.
The findings are from the watchdog's review of PSB amidst changes in technology, funding and viewing habits.
Ofcom will consult on the report before making recommendations to the government next year.
The final findings will feed into the government's own consultation into the future of PSBs, announced by Culture Secretary Oliver Dowden in November.
"There might be ways of bringing in new providers or even providers that are already there, like Netflix or Sky or Discovery, into the market," Ofcom chief executive Dame Melanie Dawes told PA.
Ofcom also suggested PSBs could engage in more partnerships - such as Britbox - which "would help PSBs better compete and connect with audiences".
It also wants new laws and rules which are fit for the digital age.
And it says while the funding of PSBs is a matter for the government, other options might include full or part-time subscription models.
Dame Melanie Dawes said in a statement PSBs were facing "a blizzard of change".
The regulator spoke to audiences of all ages across the UK as well as more than 70 industry players, including broadcasters, streamers, academics, and analysts.
Dame Melanie said: "Our traditional broadcasters are among the finest in the world.
"But television has witnessed a blizzard of change and innovation, with audiences turning to online services with bigger budgets.
"For everything we've gained, we risk losing the kind of outstanding UK content that people really value.
"So there's an urgent need to reform the rules, and build a stronger system of public service media that can flourish in the digital age."
Ofcom said its research showed that people still value public service content, despite audiences increasingly turning to global streaming.
News was seen as its most important offering, with more than seven in 10 viewers placing importance on regional news.
Viewers also want to keep seeing content made about the UK and their own area on screen, Ofcom said.
Original UK children's programming, education and religious programming, made specifically for the UK, are seen as public service content that the market is unlikely to provide.
Yet, last year, only 38% of 16 to 34-year-olds who responded (and 67% of all adults) watched traditional broadcast content, said Ofcom.
Two in five viewers of streaming services told the watchdog they could imagine watching no broadcast TV at all in five years' time.
So what might be done?
Broadcasting laws have not been updated since the 2003 Communications Act when the world was a totally different place in terms of technology.
Ofcom proposes adapting rules for broadcasting in a digital age, so that the BBC, ITV and other PSBs can appear more on online platforms.
Ofcom said other countries such as Canada and Germany had successfully changed regulations to oblige online platforms to make public service content available.
The idea of online streaming services offering PSB content was felt to be worth considering due to a fall in advertising revenue.
Ofcom suggested that subscriptions and the involvement of commercial companies could "drive innovation, bringing different insights, experience and expertise to the PSM (public service media) system".
"Encouraging established or emerging brands, potentially those which already resonate with younger online audiences, should help create an environment where risks can be taken for providing and distributing UK content for audiences of all ages," it added.
A BBC spokesman said: "We welcome Ofcom's consultation showing that public service broadcasters are highly valued by UK audiences.
"A publicly funded BBC is at the heart of a thriving UK creative sector. We're also pleased to see Ofcom's call for regulatory reform that's fit for a global, digital market place.
"We'll look at any proposals carefully and respond fully in due course."