Fans are excited about the film after seeing the trailer

The Kingdom of the Crystal Skull taster shows clips from the first three movies before cutting to an action scene of Harrison Ford swinging on his bullwhip.

One blogger said of the clip: "I feel like a kid again." Another described it as "humorous" and "brimming with ridiculous action".

The movie, co-starring Cate Blanchett and Shia LaBeouf, is out in May.

'Interesting mysteries'

Both stars also appear in the trailer - Blanchett can be seen in a black wig.

"As soon as the John Williams' Raiders overture kicks in, you cannot suppress a nostalgic smile," said one fan.

"Aside from bits of obvious CGI trickery, the trailer is nearly a note-perfect recreation of Indy's past adventures."

The clip, available on the official Indiana Jones website, has also increased speculation about the storyline.

Plot details have not been revealed

A magnetic case marked with the word Roswell, prompted one fan to suggest that "extra terrestrials somehow fit into the origins of the titular skull".

There is also a general consensus that Harrison, 65, is not too old to reprise his performance as the surly archaeologist.

"I think I watched this thing four times in a row before doing anything else. It's as wonderful as I imagined. I don't care how old Harrison Ford is, he looks great," said a fan.

Harrison, along with producer George Lucas and director Steven Spielberg, had resisted making a fourth film for almost 18 years.

However, in 2006 Lucas confirmed a sequel had been written - after more than a decade in development.

He told the Associated Press the film was "going to be fantastic" with some "very interesting mysteries".