James Franco watched Tilda Swinton sleeping in a glass box.

The 'Oz the Great and Powerful' star was among the intrigued onlookers who caught the Oscar-winning actress' bizarre impromptu exhibition - a revival of her 1995 performance art show 'The Maybe' - at the Museum of Modern Art (MoMA) in New York City on Saturday (23.03.13).

James, who was accompanied by R.E.M. singer Michael Stipe, visited the 52-year-old star's art installation just before closing time and had a front row view of the sleeping actress, according to website Gothamist.com.

Visitors quickly flocked to Twitter to express their excitement, with one writing: ''Tilda Swinton is in a glass case @moma and James Franco & Michael Stipe are looking on. Just a Sat. Afternoon in NYC. (sic)''

Another onlooker tweeted: ''Tilda was sleeping. James Franco was a part of the crowd staring. This is amazing sh*t. Made it JUST before the museum closed!! #TheMaybe (sic)''

The 'Moonrise Kingdom' actress also had fellow celebrities buzzing about her quirky showcase.

'Kick-Ass' actress Chloe Grace Moretz said: ''Cannot even begin to explain how I wish i had seen this!!! (sic)''

Comedian Patton Oswalt joked: ''Tilda Swinton is sleeping in a glass box on random days at MoMA in New York all year. And I just thought of a brilliant heist movie... (sic)''

Tilda first performed 'The Maybe' at the Serpentine Gallery in London in 1995, and again a year later in Rome.

Her appearance at the New York City museum came as a shock to museum-goers as it wasn't advertised beforehand. The actress is set to perform 'The Maybe' several more times throughout the year, but again, the museum won't be announcing her shows in advance.