China this week marks the 30th anniversary of the great Tangshan earthquake that killed 240,000 people, with survivors still in mourning and the government focusing on the rebuilding.

Lu Guilan,trapped under the ruins for 13 days, was rescued by soldiers. [Newsphoto/file]

The quake, the most deadly of the 20th century, measured 7.8 on the Richter scale and shook the northern industrial city of Tangshan to its core for 15 seconds at 3:42 on the morning of July 28, 1976.

Many who were buried alive underneath the rubble of the earthquake were killed 15 hours later when an aftershock measuring 7.1 struck.

Nearly a quarter of the then population of one million people in Tangshan, about 200 kilometers (120 miles) east of Beijing, died in the quake and its aftermath, according to official figures.

"The most horrible memory I have of the earthquake was walking through a small area that was piled full of dead bodies in plastic bags," Li Xuemei, now a book seller in Tangshan, told reporters.

"At the time, I was only seven years' old, so I don't remember a lot of things, only that it was horrible."

Eight members of Li's family died on that day, including a younger brother, three of her grandparents, an aunt and several cousins, she said.

"Things have really changed for the better in Tangshan over the last years, but still on July 28 we will not be celebrating our survival, we will only commemorate the dead," she said of Friday's anniversary when Chinese President Hu Jintao is expected to visit the city.

The quake, which produced energy 400 times more powerful than the Hiroshima atomic bomb, seriously injured over 160,000 people and destroyed 90 percent of Tangshan's buildings.

The epicenter of the quake was located eight kilometers (five miles) directly beneath Tangshan.

The disaster left 4,200 children under 16 orphaned, while 7,000 men lost their wives and 8,000 women lost their husbands. Over 7,200 entire families perished in the quake.

"It was a devastating day," said Wang Baoqin, 57, a woman who has survived to sell souvenirs and photos at Tangshan's earthquake memorial.

"That morning all we did was search and search for people. I survived without any injuries, but many in my family were killed or injured.

"I still clearly remember all the dust and flattened buildings, the screaming and wailing for help."

Wang said that the changes that have taken place in Tangshan since the earthquake were "unthinkable" 30 years ago, but still China's booming economic development and modernization drive had not replaced the pain of the quake.

Railway worker Chen Jianhua, 50, said he will never forget being buried for two hours beneath the rubble of a brick shed where he was living with other workers at a construction site.

"Other workers noticed that no one came out of our shed, so they began digging until they found us," Chen said.

After being rescued with only minor bruises, Chen walked home over 15 kilometers (nine miles) through the heart of the city, ignoring the screams of the injured and the cries for help.

"Bodies were being piled everywhere, but I couldn't stop to help because all I thought about was getting back home to see if my family was all right," he said. He was relieved to find his mother and father alive, although he lost friends and other relatives.

For the 30th anniversary commemorations, media has largely focused on the rebuilding of Tangshan into a modern-day metropolis of nearly three million people full of new buildings and wide boulevards.

With thriving steel, other metals and coal mining industries, Tangshan is one of China's top 50 cities with a gross domestic product of 54 billion yuan at the end of 2005.

The city proper is surrounded by the Tangshan prefecture made up of six districts, six counties and 7.14 million people.