An Australian tourist was killed and three others injured, one seriously, in a jet ski accident off the island of Penang, officials and reports said today.

Kathryn Sheppard, 21, from the Australian state of Victoria, suffered massive internal injuries and her companion Carlos Gonzales, 29, from Mexico, was seriously injured when the jet ski they were riding collided with another yesterday.

Two Australians on the other jet ski, Natasha Sage and Rachel Dimieri, both 20, were slightly injured and received outpatient treatment at a private Penang medical centre.

"It's a jet ski accident. They were racing each other so the accident happened. One of the jet skis hit the other jet ski," a local official who spoke on condition of anonymity said.

Police said the jet-ski ridden by Sage and Dimieri had run into that of Sheppard and Gonzales in the waters off a northern Penang beach popular with tourists.

Ribs punctured heart

"A post-mortem ... found that Sheppard died from internal injuries. The impact of the crash was so great that one of her fractured ribs punctured her heart," Penang police chief Azman Yusof was quoted as saying in the Star daily.

He said Gonzales, who suffered head and body injuries, was in intensive care.

"His condition is serious but stable," said Azman.

The four had been on a cruise ship that was in Penang for a day-long stopover en route from Phuket to Singapore, said reports.

Police, hospital and consular officials could not be reached for further comment.