HOBART, Australia (AP) _ A gun with a high-powered rifle opened fire at a popular tourist site in Tasmania on Sunday, killing at least 30 people in what police called Australia's worst massacre in modern history.

At least 18 other people were seriously injured.

The gunman barricaded himself in a cottage with at least one hostage and was firing on police trying to negotiate with him and at helicopters trying to evacuate the wounded to hospitals.

``Various massacres would pale into insignificance when you look at what has happened in Tasmania,'' said Tasmanian Police Commissioner John Johnson.

Wendy Scurr, who was working at the Port Arthur historic landing site when the gunman opened fire, told Sky News Australia that children were among the victims.

She said she called for help and then ``ran for my life along with hundreds of other people at the site.''

Victims were not immediately identified, but Johnson said, ``It won't be just Tasmanians, it will be people from other parts of Australia, and no doubt other parts of the world.''

Some 500 Australian and foreign tourists were at the site, about 30 miles southeast of Hobart, at the time. Port Arthur was the historic landing site of some of the toughest convicts England sent into Australian exile in the 1800s.

Witness Karen Jones told the Australian Broadcasting Corp. that the gunman had blond hair and appeared to be about 19 or 20 years old. He drove into the tourist site in a Volkswagen with a surfboard strapped on its top before producing the gun and opening fire.

Witnesses said he shot people in buses parked near the tollgate entry to the historic site, fired more shots at a food shop and a nearby pub, then began roaming the street shooting people at random. He set fire to some buildings and at least one car before retreating to the cottage.

``There is a lady dead in a car at the top of the drive. There's been people shot in the historic site, and there's been people shot near the Fox and Hounds (Pub),'' Phillip Kelly, a local cafe owner, told TV Channel 10.

The old prison colony is on the Tasman Peninsula, connected to Tasmania's mainland by one road on a narrow isthmus, which police closed to the public and media.

The Port Arthur site, with its preserved colonial-era buildings, is one of the most popular tourist attractions in Tasmania, an island about 150 miles south of the Australian mainland.

The scenic area boasts neat green lawns, the ivy-covered remains of a Gothic church, and the crumbling ruins of the old penitentiary, where a total of about 30,000 prisoners were held between 1833 and 1877.

Sunday's shootings were the worst massacre in Australia in modern times.

In 1987, Frank Vitkovic killed eight people in Melbourne before plunging to his death from the window of a high-rise building.

State guns laws vary in Australia, but it is fairly easy for a person without a legal record to buy a rifle or shotgun. Pistols are less commonly owned.