The Screen Actors Guild has announced it will go on strike, marking the start of the largest shutdown Hollywood has seen in 40 years.

The union wants streaming giants to agree to a fairer split of profits and better working conditions.

The walkout means that 160,000 performers will stop work at midnight.

Stars Cillian Murphy and Emily Blunt left the Oppenheimer premiere as the strike began, according to director Christopher Nolan.

The SAG strike will begin at midnight Los Angeles time (08:00 BST). Picketing will begin on Friday morning outside the California headquarters of Netflix, before moving on to Paramount, Warner Bros and Disney.

The union is also asking for a guarantee that artificial intelligence (AI) and computer-generated faces and voices will not be used to replace actors.

Additionally, the SAG is seeking tighter regulations on self-taped auditions. It believes that home auditions unfairly pass on the cost to performers.

According to a strike order published online by SAG, the walkout applies to those employed acting, singing or dancing, as well as stunt performers and those involved in puppeteering or motion capture work. The stoppage also applies to a variety of background and promotional tasks.

On Wednesday, the union - officially known as the Screen Actors Guild-American Federation of Television and Radio Artists, or SAG-AFTRA - announced it was unable to come to an agreement with major studios.

Its negotiating committee voted unanimously to recommend strike action. It means the vast majority of US film and TV productions will stop.

The group representing the studios, the Alliance of Motion Picture and Television Producers, or AMPTP, said that "a strike is certainly not the outcome we hoped for as studios cannot operate without the performers that bring our TV shows and films to life".

"The union has regrettably chosen a path that will lead to financial hardship for countless thousands of people who depend on the industry," its statement added.

To address concerns about the use of AI, the AMPTP said it had agreed to a "groundbreaking proposal" that would protect the digital likeness of actors, and require their consent when digital replicas are used in performances, or alterations are made.

The SAG's national executive director and chief negotiator, Duncan Crabtree-Ireland, said that the offer was unacceptable.

"They propose that our background performers should be able to be scanned, get paid for one day's pay, and their company should own that scan of their image, their likeness, and should be able to use it for the rest of eternity," he said. "If you think that's a groundbreaking proposal, I suggest you think again."

Fran Drescher, SAG's president, said the strike comes at a "very seminal moment" for actors in the industry.

"What's happening to us is happening across all fields of labour," she said, "when employers make Wall Street and greed their priority, and they forget about the essential contributors that make the machine run."

A separate strike by the Writers Guild of America demanding better pay and working conditions has been going since 2 May. Some writers have turned to writing projects that are not covered by the contract between the guild and the Alliance of Motion Picture and Television Producers.

The "double strike" by both unions is the first since 1960, when the SAG was headed by actor and former US President Ronald Reagan. The last strike by actors took place in 1980.

Ahead of the SAG's announcement on Thursday, Disney CEO Bob Iger told MSNBC that the demands of both the actors and writers are impractical and damaging to the industry.

"There's a level of expectation that they have, that is just not realistic," he said. "They are adding to the set of the challenges that this business is already facing that is, quite frankly, very disruptive."

A third union, the Directors Guild of America, successfully negotiated a contract in June and will not participate.

The beginning of the strike will mean that a vast majority of US film and TV productions will be forced to stop, adding to a list of projects that have already shut down or stalled because of the writers' strike.

For films already in production, the stoppage means that a large portion of work will become impossible. Even in cases in which filming has already been completed, actors will be unavailable for re-shoots and other essential elements of the filmmaking process.

TV shows that are still being filmed will also largely have to stop as actors become unavailable, although in some cases side deals could be struck between performers and producers to allow work to continue.

Top Hollywood stars will not be able to attend events to promote new and upcoming releases. Events including the Emmys and Comic-Con may be rescheduled or scaled back.

International events, such as the Toronto and Venice film festivals, will still go on, although SAG actors will be unable to attend as they do each year.

In the hours following the announcement, several SAG-affiliated actors took to Instagram to voice their support for the strike, including Better Call Saul star Bob Odenkirk, Sex and the City's Cynthia Nixon and Hollywood veteran Jamie Lee Curtis.