China has released five Christian detainees in Zhejiang province after four months in prison for protesting a church demolition.

The five, Ji Qingcao, Ji Qingcou, Ou Jinsi, Mei Xueshun, and He Lijing, are all members of Yazhong Church in Wenzhou, and were arrested in April on charges of "obstructing government administration" and "disturbing public order".

They had been involved in a protest over the planned demolition of another church, Guankou Church, in September last year.

A local Christian told human rights charity China Aid that the five had been released on August 28, and suggested it could have been due to pressure ahead of the upcoming G20 summit in Hangzhou.

"I feel like the government is trying to pacify the people before the summit meeting. Since the summit meeting will be held here [on September 4], the government begins to worry that they have detained the Christians for too long," the source said.

"The local government was concerned about petitions organised by the family members, thinking higher officials would pressure them."

It was announced in July that Chinese authorities had banned churches in Hangzhou, Zhejiang's capital, during the G20 summit "to create a safe environment".

The Global Times, a tabloid run by the ruling Communist party, said large-scale religious meetings had been blocked "to create a safe environment for the meeting".

The US-backed Radio Free Asia reported that the city's unofficial churches had also been told to stop meeting. "They have been forcing house churches not to meet ahead of the G20 summit," said Zhang Mingxuan, the president of China's House Church Alliance.

Activists have cautioned that the move may be part of a wider crackdown on churches in Zhejiang.

Up to 1,700 churches have been demolished or had their crosses removed in the province over the past two years.