There will be an empty chair – and a big gap in the agenda – when many of the world’s leaders gather in Italy this week.

Chinese President Hu Jintao abruptly returned home from Italy even before the summit started, rushing back as ethnic tensions in Western China have erupted in violence.

That means President Barack Obama will not have a scheduled meeting Thursday with Hu, and he and other Westerners will have to wait to press their case at the highest level for Chinese concessions on such thorny issues as global warming and North Korea’s moves to develop nuclear weapons and long range missiles.

Chinese State Councilor Dai Bingguo will attend the summit in Hu’s place, but won’t have the stature of his president.

“We have a broad based agenda with China,” Michael Froman, the White House deputy national security adviser for international economic affairs, said Wednesday at the summit site in L’Aquila, Italy.

“Since this meeting didn’t happen,” he said of the Obama-Hu summit, “they look forward to the next meeting.”

China is key to several of the top issues facing world leaders, including forging a global response to global warming and pressuring North Korea to stop its moves to become a nuclear power.

In addition to meeting one-on-one with Obama, Hu was supposed to be one of the leaders attending the Major Economies Forum hosted by Obama that will discuss global warming. Thus far, fast-growing China has resisted calls to cut its emissions of greenhouse gases from smokestacks and tailpipes.

China also has refused to go along with tough economic sanctions against North Korea, one of its trading partners.