MANILA, JULY 16 -- A powerful earthquake shook Manila and neighboring provinces on Luzon Island today, devastating schools and luxury hotels, cutting power and telecommunications lines and trapping hundreds of people beneath rubble. At least 150 people are known to have died and more than a 1,000 injured as of late tonight, and the toll was expected to rise.

The quake measured 7.7 on the Richter scale, according to the U.S. Geological Survey in Golden, Colo., the strongest to hit the Philippines in 14 years and at least as strong as the temblor that left tens of thousands dead in Iran last month. Today's quake, which struck at 4:30 p.m. (3:30 a.m. EDT), lasted about 45 seconds and was followed by numerous aftershocks, the first two nearly as strong as the initial tremor.

Interrupted communications and a shortage of heavy equipment -- especially bulldozers and other machines to clear away collapsed concrete and other debris -- was hampering rescue efforts, and casualty counts differed among various government agencies. All agreed, however, that more bodies were certain to be found as rescue and salvage crews burrowed beneath shattered buildings across the stricken region.

Most deaths and injuries reported so far have occurred in areas about 50 to 120 miles north of Manila in central and northern Luzon, the largest of the more than 7,000 islands that make up the Philippines. At least 53 young students died when a six-story building housing a Philippine Christian school collapsed in the provincial capital of Cabanatuan, 55 miles north of Manila in Nueva Ecija province, the epicenter of the quake.

About 50 students and teachers trapped in the wreckage of the building were rescued when a crane was brought in to lift away the debris. Others, buried in the rubble and crying for help, were pulled to safety by soldiers and rescue workers, but authorities said hundreds more may still be buried there.

"We were going down the stairs when we noticed that it was collapsing," 13-year-old Edralin Dino told the Reuter news agency. "It {the school} kept shaking. Then the hollow {concrete} blocks came down on us. We were about 80 in all, and we ran. I saw headless bodies on the ground. Some of us were vomiting blood. Many were moaning for help. Many were trembling."

Baguio, a coastal mountain resort of about 120,000 people 110 miles due north of Manila, was heavily damaged and the death toll could rise significantly there. Twenty-three people were reported killed when a building at the University of Baguio collapsed, and at least 10 died when the downtown produce market was flattened. Scores of other buildings were damaged, and sections of at least four luxury hotels caved in, injuring hundreds of people, including an unknown number of vacationing foreigners.

At the Hyatt hotel, a favorite with foreign tourists, about 50 people were reported dead and 150 others were believed still trapped after eight or nine floors of a new wing collapsed. The Nevada Inn in Baguio also collapsed, trapping about 100 people, and rescuers there were said to be especially concerned because they could hear no calls for help from beneath the debris, as they had in other areas.

Scores of guests were also believed trapped in rubble at two other heavily damaged hotels, and the Phillipine military said that 800 more people were thought to be caught beneath debris at a government building in the Baguio Export-Processing Zone. A building in Baguio owned by the Texas Instruments company was reported demolished.

U.S. officials said many of those injured in Baguio were being transported to American military hospitals at Camp John Hay and Clark Air Base. They said there were unconfirmed reports that two of the dead were Americans. "The hospitals are full, and I saw many injured foreigners," said one reporter in Baguio in a radio link-up broadcast to radio station DCRH in Manila.

{In Washington, State Department spokesman Richard Boucher said U.S. officials were investigating a report that an Agency for International Development conference was underway at a hotel in Baguio when the quake struck and that at least one participant had died.

{Boucher added that U.S. ambassador Nicholas Platt had contacted Philippine President Corazon Aquino and committed $25,000 as a first step in disaster relief from the United States.

{The Pentagon announced, meanwhile, that it had provided an Air Force C-141 transport plane to carry American civilian rescue workers, dogs and equipment to help in the hunt for survivors. Among those making the flight will be a search and rescue team mobilized by the Fairfax County Fire Department.}

In Manila, President Aquino appealed for calm, suspended all public school classes until Tuesday and ordered military and provincial officials to give all emergency aid available to the earthquake victims. "Let us pray to God to keep us safe," Aquino said in a nationwide television address.

The quake struck while Aquino was meeting with Senate President Jovito Salonga, and she said she sought protection under a table. "I did not think it was something to panic about, but I hoped it would end soon," she said.

At least two people died in Manila, which together with its close-in suburbs has a population of 8 million. At least 16 were injured in a stampede at a suburban shopping mall as the tremor drove panicked people out of stores, theaters, offices and restaurants, and at least one hotel, the Bayside Manila, was evacuated.

"We also abandoned the police headquarters," said Manila Police Sgt. Rufino Bautista. "We were scared."

The temblor knocked radio and television stations off the air, disrupted all cable-carried communications systems and left tens of thousands of motorists stuck in miles-long backups as traffic signals failed all over the capital. Many more thousands of people were stranded when the quake shut down power to the city's commuter rail system.

Large fissures opened in the walls of numerous downtown buildings, including the main Philippines Airlines office and the Manila Film Center built by former first lady Imelda Marcos. Windows were shattered throughout the city, and officials were examining structures near Malacanang Palace, where the president holds office, to see if they were safe for occupancy.

In Pangasinan province near the capital, at least seven people died in a panicked rush to flee a crowded movie theater, and many families chose to camp out overnight in open areas for fear that another strong quake might trap them in building ruins, Reuter reported.

In addition to the deaths at the Christian school in Cabanatuan, three children were said to have been killed in the collapse of an old grade-school building and four other people as buildings crumbled in Cabanatuan's urban center.

Paved roads and bridges throughout the affected region buckled or were seriously weakened, and the main route from Manila to Baguio -- built by the Americans after World War II -- was declared a danger zone.

The quake was the most powerful to hit this country since 1976, when a temblor measuring 7.8 on the Richter scale killed 8,000 people, many drowning in a tidal wave that hit the southern island of Mindanao. Today, northern coastal provinces such as Pangasinan, Ilocos Sur and Cagayan were warned to take precautions against the possibility of tidal waves, but there were no reports that any had struck.

Staff writer Margie G. Quimpo contributed to this report in Washington.