BEIJING — On the 10th anniversary of China’s deadliest earthquake in decades, the police on Saturday detained an outspoken pastor and blocked a planned service to mourn the 70,000 or more people killed when whole towns and villagers were crushed.

The anniversary of the earthquake, which rippled across Sichuan Province in southwest China on May 12, 2008, has been a time of renewed mourning for survivors, while the ruling Communist Party has used the date to praise China’s reconstruction of devastated areas.

But officials in Sichuan have sought to stifle any unapproved commemorations that could rekindle angry questions about why many new buildings, including schools, collapsed in the 7.9-magnitude quake.

On Friday night, the police detained Wang Yi, a Protestant pastor whose independent church planned to hold a memorial service on Saturday morning in Chengdu, the provincial capital of Sichuan, his wife, Jiang Rong, said.