Tens of thousands of Hollywood actors are preparing to strike after last-ditch talks between their unions and streaming giants broke down just hours before a major deadline.

The Screen Actors Guild (SAG-AFTRA) has agreed to one extension of talks with major studios.

But the union has been unable to agree a deal over issues around pay residuals and the use of artificial intelligence.

On Thursday, it is expected to decide to join screenwriters on picket lines.

Writers have been striking for several months, outside the studios of major streamers including Disney, Netflix and Paramount, over pay and work conditions.

The negotiating committee of SAG-AFTRA, the union which represents 160,000 actors and performers, voted unanimously to recommend strike action to its board.

It had been seeking a fairer split of streaming profits and a guarantee that AI will not be used to replace duties performed by actors.

"We are not confident that the employers have any intention of bargaining toward an agreement," the committee said after Wednesday's midnight deadline passed.

"Time is running out," it warned.

The guild's president, Fran Drescher, accused streaming companies of refusing "to meaningfully engage on some topics and on others completely stonewalled us".

The group representing the studios, the Alliance of Motion Picture and Television Producers (AMPTP) said it was "disappointed" by the collapse of negotiations.

"This is the Union's choice, not ours," the AMPTP said in a statement.

"In doing so, it has dismissed our offer of historic pay and residual increases, substantially higher caps on pension and health contributions, audition protections, shortened series option periods, a ground-breaking AI proposal that protects actors' digital likenesses, and more."

Hollywood has not seen a "double strike" of actors and writers since 1960, and the joint move would see almost all US film and TV productions grind to a halt.

The strike could also extend to the UK and other countries where members of the acting union are active on film sets.

It would also prevent A-listers from promoting some of the year's biggest releases.

US publication Variety has reported that Thursday's London premiere for Christopher Nolan's Oppenheimer has been brought forward by an hour so that stars such as Robert Downey Jr, Emily Blunt and Matt Damon can attend without breaking a union deadline for a decision about a walkout.

A strike could rule them out of the film's big US premiere in New York on Monday and beyond, while other major film and TV events like next week's annual Comic-Con event in San Diego could also be scaled down.

But top actors have already made it clear that they are willing to strike. In June, a letter from A-listers including Meryl Streep and Jennifer Lawrence urged the union not to settle for a mediocre deal.

The union for the collective studios, the AMPTP has reportedly called in federal mediators to help resolve the deadlock.

On the other side, Hollywood unions representing directors and crews issued a statement of "unwavering support and solidarity" with the actors on Wednesday.