GETTYSBURG, United States (AFP) - In a field of tall grass, shots ring out and puffs of smoke rise as soldiers re-enact the Battle of Gettysburg and America begins to mark the 150th anniversary of that turning part in the Civil War.

Some 200,000 history buffs are expected to trek to this corner of Pennsylvania over the next 10 days to relive what happened here between July 1 and July 3, 1863.

The deadliest battle ever on US soil with nearly 8,000 dead and tens of thousands of injured, it delivered a fatal blow to the Confederates and marked the start of the southern army's retreat. The war, however, would only end two years later.

"Let's draw sabres again," called out a Union cavalryman clad in blue - the colour of the North - his flag flapping proudly in the wind.

Wearing a grey cap - the color of the South - John Baldwin exuded enthusiasm, calling the re-enactment "fantastic." The 61-year-old said he came here in the name of his ancestors, who were Confederates from North Carolina.

"When you read the books, you don't see the distance and how far away the soldiers are, how large the battlefield is," he said.

About 25,000 "re-enactors" are on scene, fully decked out in period garb to personify those present at the historic event all those years ago - General George Meade for the North and General Robert E. Lee for the South, as well as civilians and soldiers galore.

James Taub, wearing a blue woolen vest with buttons from the time that boast the emblems of the Union, is playing the role of an infantry soldier.

"It's like getting reconnected to the past," said the 20-year-old history student from the state of Michigan.

Nearby, women in hoop dresses twirl lace parasols on their shoulders as they stroll among an encampment consisting of large white tents.

A big draw is a stand displaying weapons of the time. Here, participants can buy muskets, sabres or pistols for use in the re-enactment. But they won't be using real bullets - just black powder.

Even children are called to action - "Enlist Now!" - with youngsters able to try on uniforms and handle wooden weapons.

And then there are nurses like Meredith Eng, who called out to the soldiers to "Enjoy the war!" Decked out in a large grey hat and a colonel's uniform, Frank Orlando is one of several people playing Lee.

"Everything my wife and I will be wearing is historically accurate," he said. That even includes the buttons on his uniform, produced in his home state of Virginia.

"He might have lost the war, but he led the people of the South through reconciliation and reconstruction," Mr Orlando said of Lee, comparing him to Napoleon.

Donning a blue cap, Conor Timoney, an 18-year-old from Philadelphia, chose to personify a Union soldier because "I couldn't fight against the American flag." For Orlando, meanwhile, "history is written by the victorious." "All the people of the North they think that there was one cause that was slavery" when what the South was really after was independence, he said.

"All we wanted to get is independence." Historian Brian Jordan pointed out the limits of re-enactments as a historical tool, which are very popular in the United States.

"In that search for finding the right uniform and the right gun, and re-enacting the best emotions of the war, they can escape that fundamental reality that it's about slavery," he said.

Tony, a young African American from Virginia who admits not knowing the history of Gettysburg, wondered why there were "very few" blacks in the crowd.