President Barack Obama has been urged to raise the issue of religious freedom in China when he visits next week for the G20 summit.

Obama will be in Hangzhou, capital of Zhejiang province, on September 4 and 5. The province has been the focus of a months-long campaign to remove hundreds of crosses from church buildings, although this persecution has lessened recently.

The United States Commission on International Religious Freedom is calling on Obama to raise the issue of religious freedom with President Xi.

The commission also wants him to press for the release of prisoners of conscience.

Thomas Reese, the Jesuit chair of the commission, said: "As the Chinese government aggressively asserts itself on the global stage, at home it aggressively violates the human rights and religious freedom of its citizens.

"While these violations have intensified in Zhejiang Province, the location of the G20 summit, they also are taking place throughout China as the government seeks to repress the voices of individuals and groups advocating for their rights."

Large numbers of Christians live in Zhejiang.

Churches in Hangzhou have already been closed in advance of the G20 because of alleged security concerns and religious activities in all hospitals have been banned. Underground churches have also been ordered to cease activities.

The commission said that the Chinese government is continuing to use forcible disappearances, torture, detention and imprisonment to crack down on all religions.

Prisoners of conscience include Bao Guohua and Xing Wenxiang, imprisoned this year for opposing cross removals.

Bob Fu, president and founder of China Aid, which campaigns for persecuted Christians in China, was one of the seven religious freedom and human rights experts and family members invited to help prepare and advise Obama for his visit to China.

Fu told Christian Today: "As I explained to President Obama's National Security Advisor Ambassador Susan Rice during our meeting in the White House on Tuesday afternoon, the religious freedom and human rights situation in China has been the worst since the time of Chairman Mao's Cultural Revolution in 1960s.

"President Obama and his Administration have failed the millions of persecuted Chinese freedom fighters and religious minorities in the past seven years by pushing these issues on the back seat of his foreign policy agenda to China.

"He should take this as his last opportunity to do something beyond the norm to not only raise cases of numerous arbitrary arrest of pastors, bishops and rights defenders, but more importantly to make a strong public statement along with our allies during his trip in Hangzhou to reaffirm American's long term commitment on the vital link between religious freedom, human rights and civil society with sustainable economic prosperity and international security.

"The whole world will watch whether President Obama will lead courageously for this effort during the G20 summit."