Grieving Chinese parents said on Wednesday they will press forward with protests against officials they blame for schools that toppled in a devastating earthquake a day after police sought to silence complaints.

The quake centred in southwest China's Sichuan province has killed 69,107 people with many thousands missing and likely dead, according to the latest official figures. Many parents of the 9,000 or more children killed blame flimsy schools and the officials who they claim ignored building safety rules.

In Dujiangyan, a small city near the Sichuan province capital Chengdu, some of those parents vowed to keep up their complaints a day after police prevented some 150 of them from seeking to lodge a lawsuit over a collapsed middle school.

"The government has said it will address our complaints, but the officials are too corrupt to actually do anything," said Zhao Deqin, a mother whose 15-year-old twin daughters, Yajia and Yaqi, attended the Juyuan Middle School and were in a building of classrooms that collapsed, killing hundreds of pupils.

"Many lawyers have offered to help us, and we're going to certainly sue the government and the school."

Officials have said more than 200 children at the school died, but parents say 400 or more may have been killed and pointed out that apartments nearby stayed upright while the school building fell. With China's "one-child" population controls, many parents lost their only offspring.

On Wednesday, the area around the school was guarded by troops. One tearful couple nearby said their son had died there in the quake and today would have been his 16th birthday.

"We'd like to file a lawsuit," said the man, surnamed Zheng, who showed his late son's identity card. "It's all this tofu dregs building," he said, using a Chinese phrase for shoddy construction.

In past days, some Chinese newspapers have reported on the many schools that fell, citing experts who have blamed brittle concrete, thin or non-existent steel reinforcement and improperly positioned pillars.

But the protests by parents have not been reported locally, and efforts by officials to discourage foreign reporters talking to parents underscore the sensitivity of the school issue when the government wants the focus on massive relief efforts for millions of displaced people.

"This is going to be a touchstone issue that brings together questions about how to deal with the quake aftermath - accountability, the public interest and compensation," Xu Wu, a former Chinese journalist and now a public relations expert at Arizona State University, said of the schools.

"Normally four to five weeks after a disaster, relatives of victims recover from the initial shock and become more demanding and questioning. I think that will start happening."

In Beijing, lawyers have held meetings on the rights of quake victims and issued calls for a thorough inquiry into the schools.

"That it was school rooms that collapsed first in the earthquake is a national disgrace," rights campaigner Xu Zhiyong told a recent forum, according to a transcript seen by Reuters.

Relief workers continued to search for a crashed military helicopter and guard against dangerous quake lakes. There were 19 people aboard the aircraft, including 10 injured quake survivors.

Troops and disaster officials have also been seeking to defuse threats from the more than 30 unstable "quake lakes" created by quake-caused landslides choking rivers and endangering hundreds of thousands of people downstream.

Authorities must be on high alert against lightning attacks on tents and pre-fabricated housing units, which had been going up across the region sheltering millions of homeless quake refugees, the centre said on its website (www.nmc.gov.cn).