Five years after thousands of Chinese children died as their schools collapsed in an earthquake, new babies have given devastated families hope even as questions over poor building work and corruption remain.

The 8.0 magnitude tremor struck Sichuan province on the afternoon of May 12 2008, entombing both Zhu Jian's wife, a teacher, and their 10-year-old daughter in the rubble of their school in Beichuan, the epicentre of the quake.

Zhu's wife Liu Lin was pulled from the debris severely injured, and was left disabled, but the disaster killed their daughter, whose name the couple -- bearing deep psychological scares -- are unable to speak.

They were in one of 7,000 schools that were badly damaged in the southwestern province, triggering accusations of shoddy construction, corner-cutting and possible corruption, especially as many other buildings nearby held firm.

Statistics from the local education department showed that 3,340 schools needed to be rebuilt.

To this day Liu Lin, 38, is too traumatised to talk about her ordeal. But the couple have renewed optimism following the birth of their son Zhu Tian two years ago.

"Having a child is having hope, and without children there is no hope," said Zhu, a police officer who rebuilt the family home using 100,000 yuan ($16,000) in savings, plus government handouts.

Authorities said 5,335 pupils in Sichuan were confirmed as dead or missing. At Beichuan Middle School alone, 1,300 students and teachers lost their lives.

For many parents China's one-child policy meant the implications -- and the pain -- were particularly severe. The quake left 8,000 families childless.

The government adopted a series of measures to encourage them to have new children, including free reverse vasectomies, and about 2,400 babies have been born to them since.

"We just had to have a descendant. That is the way in China," said Zhu, whose wife was able to claim free maternity treatment.

But he declined to be drawn on the mistakes of the past, preferring to focus on life after the disaster.

Asked whether he believed any blame could be attached to authorities for the collapse of buildings in Sichuan, Zhu paused in thought. "The government have done a good job rebuilding the area since the earthquake," he said.

Many are still seeking answers on how the quake destroyed so many schools when it struck during afternoon classes. They have become known as "tofu schools" in China, likening their structural instability to the popular soft bean curd dish.

No-one appears to have been prosecuted over the school collapses. But calls for transparency from the government on how many students were killed led to beatings and arrests of activists.

Among those targeted were dissident artist Ai Weiwei, who said he was badly beaten by police when he tried to testify in support of activist Tan Zuoren, who had investigated the school buildings.

The earthquake aftermath marked the emergence of Ai -- chosen by the authorities to help design the Bird's Nest Stadium in the Chinese capital which hosted the Olympics athletics events three months after the tremor -- as one of Beijing's most outspoken critics.

"I have made documentary films and artworks relating to it," said Ai, who organised a citizen's probe into the school collapses. "This is to remind people they have to respect life and also to refuse to forget what happened."

Other prominent campaigners have signed an open letter circulating online calling for the release of Tan.

The writer and environmentalist was sentenced to five years in prison in 2010 for "inciting subversion of state power" over articles he published online about Beijing's brutal crushing of the 1989 Tiananmen protests.

Ai said: "The government tried to cover things up and to settle the situation by jailing those people who demanded the truth, and since then they never really learned anything from it."

But for Zhu and his wife, their experience has left them seeking only a future for their son.

"We just hope he is healthy, and we have nothing else to ask from him," Zhu said.