In China's remote north-western province of Xinjiang, Muslim faithful stream into the Id Kah mosque in Kashgar, 3,500 kilometres from Beijing.
But to answer the call to prayer in Xinjiang, home to 11m Muslims, is to enter the latest battleground in China's war against terrorism.
As worshippers bow towards Mecca, their devotion is clear. It is the form that devotion might take which worries the Chinese authorities.
China is worried about how to control its Muslim minority
The top official in Xinjiang, Communist Party secretary Wang Lequan, spelled out his priorities.
"Religious extremism is one of the three forces in Xinjiang that we are making great efforts to fight against," he said.
"The other two are ethnic splittism and violent terrorism. Of the three, religious extremist forces account for the most part of our efforts."
To that end, the authorities have tightened their control on religion, instituting a programme of patriotic education for the imams in all mosques in Xinjiang.
The imam at Id Kah mosque, Mohammed el-Amin, described the sessions.
Ethnically Turkic Muslims
Made bid for independent state in 1940s
Sporadic violence in Xinjiang since 1991
"We hold meetings with the religious branch of the Chinese government," he said. "They teach us about patriotism, cooperation between religion, and government and unity."
To demonstrate the forces it is fighting, local government officials took us to an exhibition about terrorism in the town of Khotan, historically a centre of anti-Chinese activity.
We were shown rusty knives, ancient guns and large quantities of grenades, confiscated - we were told - from terrorist groups.
Alongside were books and videos about Islam. One local official, Mochtar Wusur, was quick to make the link.
"Religious extremists are using the banner of religion to carry out terrorist explosions," he said. "All the books we have here are opposed to the government and reactionary. Their content is very unhealthy and very bad."
Officials are quick to link violence with religion
Pinned up on the wall were pictures of the mangled aftermath of bomb explosions and bloody corpses of murder victims. Chinese authorities say separatist groups have mounted more than 200 such attacks since 1990, causing 162 deaths. They say officials and religious personnel were targeted, including those accused of collaborating with the Chinese.
The Chinese authorities mainly blame a shadowy group called the East Turkestan Islamic Movement (ETIM). It accuses ETIM of having links to the Taleban in neighbouring Afghanistan and Osama bin Laden's al-Qaeda network, but has produced no supporting evidence.
Beijing has outlawed ETIM for a decade. After Chinese lobbying, the group was also banned last year by the US and the United Nations, despite criticism from diplomats who described ETIM as defunct. But international concerns about China's actions have largely been swept aside as the world wages war on terrorism.
Now human rights groups say that the controls on religion have gone too far.
"Any religious activity, any publication, any forum, any association which is not formally approved by the government is technically illegal in China," says Nicholas Becquelin from Human Rights in China.
"Certainly since 11 September, what we've seen is that anyone steps over that line is immediately arrested and detained and even sentenced in some cases. The policies that we see carried out in Xinjiang are a complete negation of the freedom of religion. That is absolutely certain," he said.
Religious repression could stoke popular anger
On the streets, life seems to carry on as normal. But hurried comments away from government minders indicate an undercurrent of fear and unhappiness.
"It's really bad living here", I was told by one man, a member of the province's Uighur ethnic majority. "We're being rounded up and taken away." He was too scared to say any more.
There are no figures on the number of arrests. But human rights groups overseas estimate that thousands of Uighurs have been detained since 11 September, many for illegal religious activities.
One Uighur agreed to meet in secret. To him, the war on terror has become a war on Islam.
"They're punishing people for their religious beliefs," he said. "They're punishing those who become devout Muslims and want to research Islam by themselves. Uighur people are not terrorists. They don't want to be terrorists. They're peaceful people."
The danger is that any religious repression by the authorities could stoke bitter resentment against Chinese rule.
And that could overflow into the very type of unrest that the government so wants to avoid.