"I can tell you the three of us are extremely moved to have the opportunity to sing at the Forbidden City, which is a symbol of the culture of China," Carreras said in Beijing on Thursday.
But some Chinese locals have expressed shock at ticket prices.
Opera's most famous tenors, José Carreras, Placido Domingo and Luciano Pavarotti, are due to perform on Saturday in the ancient palace of China's Emperors.
But seat prices of between $60 (£42) and $2,000 (£1,420) are beyond the reach of most Chinese although one online retailer reports they are almost all sold, with many of the tickets being snapped up by the Hong Kong Chinese.
The trio, who sing for the first time in China, say they are honoured to perform in the city.
"I can tell you the three of us are extremely moved to have the opportunity to sing at the Forbidden City, which is a symbol of the culture of China," Carreras said in Beijing on Thursday.
The concert, which will rank as China's most expensive musical event ever, is scheduled for three weeks before the host of the 2008 Olympics is chosen and is to be held on International Olympic Day.
'Recognised'
Pavarotti said their performance was their statement of support for Beijing's bid to host the Games.
"I think Beijing deserves the Olympics in order to be with all the rest of the world, recognised," he said.
While admitting that initial ticket sales were poor, Wang Long, a spokesman for the organiser, the quasi-governmental China National Culture and Art Co Ltd, said that the performance itself was only part of the point.
"It's a chance for China to show the world the progress it's made in reform and opening," he said.
But the Chinese have expressed shock at the ticket prices.
"Only the rich can afford to see it; how can average people afford such prices?" said Ling Shying, an elderly woman who collects plastic bottles and resells them for about 1.2 cents (less than a penny).
"I just hope they will let me in on the night of the performance so I can collect discarded bottles," she added.
The Tenors have given China a discount on their usual fee, but the cost is still estimated at around $10m (£7.1m).
The city has also added two sites to see the concert simultaneously broadcast on big-screen television, at the relatively inexpensive price of $9.70 (£6.60)