New York: Hollywood actress Scarlett Johansson was spotted "flirting up a storm" with 'The Hangover' star Justin Bartha, sparking romance rumours.

The 'Avengers' star, whose divorce from Ryan Reynolds was finalised earlier this month, attended the opening of Justin's play 'All New People' in the Big Apple on last Saturday before joining him for a cast dinner at Cafe Un Deux Trois where they apparently only had eyes for each other, according to reports.

"There were about 15 people at the table, but Scarlett and Justin sat next to each other and talked all night.They seemed pretty fascinated with each other and only talked to each other. It looked sometimes flirty, but also they seemed to be involved in a deep discussion. They were completely engrossed in each other," a witness said.

Bartha, 33, has been single since splitting from designer Ashley Olsen in March after a two-year relationship, while Johansson's brief three-month romance with Sean Penn recently ended.

Meanwhile, Johansson's ex-husband Reynolds is reportedly dating Charlize Theron.