Charlize Theron and Sean Penn spent the New Year’s holiday together at his beachfront property in Oahu, Hawaii and reports suggest the two Oscar winners may be more than friends.

The actress, 38, was on the island without her 2-year-old adopted son Jackson and was spotted sunbathing while Penn, 53, surfed on Tuesday, Dec. 31. They relaxed on the beach side by side and an eyewitness described the pair as "very close and comfortable together."

Earlier on Monday, Charlize was spotted strolling along the shore wearing a bikini with black bottoms and a brightly coloured, striped top.

See photos here of them in Hawaii.

They flew back to Los Angeles on the same Wednesday flight, though they separately made their exit through the terminal at LAX, and were seen at her house the next day. Photographers snapped shots of Penn leaving Theron's Hollywood home Thursda morning driving a V8 Nissan Titan truck, and following him was Theron in a black Lexus.

The two stars have been friends for years, often dining together even during Theron’s long relationship with Stuart Townsend, according to GossipCop. Reps for both stars have no commented on their relationship status.

Penn was married to Madonna and Robin Wright, and dated actress Scarlett Johannson. Theron is known to keep the details of her love life private, especially since her 2010 split from nine-year boyfriend Irish actor Stuart Townsend.