If it's spring, the Philadelphia Orchestra must be headed for China.

In the third year of its five-year agreement with the National Centre for the Performing Arts in Beijing, the orchestra opens its 21/2-week tour there on May 21, travels on to Shanghai, then plunges into less-well-charted cities - and formats - before ending with traditional concerts in Tokyo and Taipei, Taiwan, concluding June 5.

The provincial Chinese cities include Changsha and Shenzhen, where few if any American orchestras have performed. They were chosen in part because of the new Tan Dun multimedia work Nu Shu: The Secret Songs of Women, which will be performed. Given its U.S. premiere this season by the Philadelphia Orchestra, the piece preserves local folk cultures. The addition of concerts in Japan and Taiwan, which have not been part of the most recent Asia trips, was prompted partly by desire to see music director Yannick Nézet-Séguin.

"It made sense to continue the tour," said Ryan Fleur, executive vice president of orchestra advancement. "It's Yannick's first tour with the orchestra . . . and there was enough demand."

Residency activities (since China visits are meant to be more than just city-to-city tours) are still falling into place, though the orchestra hopes to have an event with the women who speak the ancient Nu Shu language in Tan's Secret Songs, and who were recorded in a village outside Changsha (where the composer once lived). Tan, who is supervising the multimedia apparatus required by the piece, carries the title of artistic adviser of the tour.

The tour will have particularly numerous joint-ensemble concerts where Philadelphians will play on the same program, and sometimes side by side, with local orchestras, starting with the chamber music concert that opens the tour May 21 in Beijing. Other such dates include a May 26 concert with the Shanghai City Symphony Orchestra, and on May 31 with the Macau Orchestra. Also discussed are reading sessions of new works by Chinese composers.

"It ties into the larger notion of people-to-people exchange," Fleur said. "It's a very actual way to connect and a very symbolic way. It's a big lift to the local orchestras . . . and, I believe, has a lasting impact artistically."

Two concerts will be available to a wider audience: The May 25 date will be webcast by Xinhui Media Group, allowing viewers to chose one of nine cameras in the Shanghai Grand Theatre. The June 3 concert at Tokyo's Suntory Hall will be recorded for later radio and television broadcast by NHK, the Japanese public broadcasting network. Both concerts will feature Nézet-Séguin conducting Mozart's Symphony No. 41 and Mahler's Symphony No. 1. The other big work on the tour is Tchaikovsky's Symphony No. 6.

In the post-bankruptcy era, these Chinese visits have been arranged directly by the orchestra, and so far, officials say, have broken even or added some earned income.

The slowdown in the Chinese economy has yet to have an impact, though the performing arts centers are mostly funded by local governments.

"The Chinese are always very tough negotiators . . . but we haven't heard anybody talk about the effects of the slowdown," Fleur said. "It's all relative. The economy is still growing by 7.4 percent."