BEIJING, China (CNN) -- A strong aftershock hit already devastated southwestern China Friday, triggering landslides, blocking roads, knocking out phone lines and burying vehicles, state-run media reported.

The 5.5-magnitude earthquake rattled eastern Sichuan province shortly after President Hu Jintao arrived in the quake zone on Friday to get a first-hand look at the devastated region.

It was just the latest of dozens of tremors that continue to fray nerves across the region.

As frantic search-and-rescue efforts entered a fifth day, the official death toll issued by authorities now stood at 21,500, with 159,000 injured, although China's state council said Thursday that it could eventually top 50,000, according to state media.

Yet hope still emerged from amid the horror of the nation's worst disaster in recent years, with survivors pulled from the rubble four days after being buried by the 7.9 magnitude earthquake that rocked southwestern China Monday afternoon.

Rescuers pulled a student from the debris of Beichuan Middle School, 80 hours after the quake collapsed the building, China's Xinhua news agency reported.

Two more people were saved after being buried for 95 hours, the agency added.

Rescuers said they could hear a weak yell for help from under the building's rubble and are "expecting more miracles," according to state-run media.

Hu flew to Mianyang in the hard-hit Sichuan province, which has become a massive refugee camp for survivors, China's Xinhua news agency reported.

"The challenge is still daunting, the task is still arduous and the time pressing," Hu said.

Thousands of people who were uprooted around the region have taken shelter at the city's main sports gym and other facilities. Reports say 7,395 people have died and 18,645 are trapped in debris in the city.

Xinhua reported 135,000 Chinese troops and medics are involved in the rescue effort across 58 counties and cities.

The scope of the operation is such that Beijing has allocated until now nearly $5 billion for the rescue relief fund.

Search-and-rescue help is also coming from outside the country. A team from Japan entered Sichuan province early Friday, Xinhua reported. Rescuers from Russia, South Korea and Singapore were expected to arrive soon.

Saudi Arabia, the United Kingdom, Germany, Vietnam and Poland were among the countries providing humanitarian assistance, according to Xinhua.

Attention is now also switching to preventing the possible spread of disease, with 60 funeral workers being sent to Sichuan province to cremate thousands of bodies, according to Xinhua.

Leading the country's disaster response, Chinese Premier Wen Jiabao praised the country for its "efficiency and order" in the midst of the disaster.

"Saving lives is still our top priority, as long as hope of survival still exists," Wen said, according to Xinhua.

But hope is running out for many trapped under tons of debris. The scene was especially painful in Beichuan, were parents of middle-school students waited Thursday, hoping recovery teams would pull their children alive from the rubble of a middle school.

They found little hope as search teams pulled out one lifeless body after another.

"There are teenagers wearing jeans and gym shoes and their bodies are twisted," CNN's John Vause said, reporting from just outside the school. "The expression on one girl's face was just pain -- she was dead."

Similar scenes unfolded out across a vast expanse of southwestern China.

A few roads to Wenchuan county -- the epicenter of the quake -- started to open Thursday, allowing military trucks to begin their haul to affected sites, while rescuers continued attempts to save those trapped beneath the rubble at schools, businesses and homes.

Late in the day, a quake-damaged road from Lixian county into Wenchuan opened after around-the-clock repairs were completed, according to Xinhua.

Rescuers have been struggling to reach the worst-hit quake areas, battling landslides, buckled roads, collapsed bridges and inclement weather.

More than 4.3 million homes collapsed or sustained damage because of the quake, according to the Chinese Embassy in Washington.