General Douglas MacArthur supposedly called Manila after the 30-day battle to take the city, "the most devastated city in the world, next to Warsaw.” Obviously, he wasn't aware of Nanking, China.

Historians say that Rape is a strong word but it still wasn't strong enough to described what happened to the city. The Americans arrived hoping to take it easy but the Jap naval commander in-charge had other plans. He thought it better to fight to his last man and, if need be, the last resident of the city.

There were other cities in the world that had been devastated, but their devastation was not a rape. Hiroshima was destroyed in a few minutes by one atomic explosion. It was destroyed “cleanly”—using that term in the sense of the American expression “to cut clean.” Coventry in England and Dresden in Germany were destroyed by one bombing raid from the air. Parts of London, Berlin and Tokyo were destroyed in several raids, each lasting no more than a few hours or even less. Manila, on the other hand, was destroyed piecemeal, building by building, street by street, district by district; a very large part of Manila’s inhabitants were killed, not by one atomic explosion or a few air raids, but individual by individual, group by group, by bayonet or bullet or by being imprisoned in sealed rooms for slow suffocation.

In that sense, Manila was the most devastated city, perhaps far more than even Warsaw.

Even before the actual battle of February and March 1945, the killings had already started. It was not the act of unruly subordinates. It was ordered from the top by the highest authority. The commander in chief, General Yamashita, declared that all male Filipinos, 14 years old and up, were “guerillas” and therefore must be killed. The systematic “sonings” of Manila, when a district would be sealed and all the males rounded up and bayoneted, corresponded to similar massacres perpetrated by the Japanese in the provinces, notably Batangas and Laguna.

But the most frightful killings were in February and March. Houses would be set on fire, and as the inhabitants rushed out, they would be gunned down or bayoneted.

At La Salle on Taft Avenue, the Brothers (who were Germans and therefore Japanese allies) and the many civilians who had taken refuge in the building were pursued from floor to floor. Many were killed in the chapel. It is said that the Japanese had sexual intercourse with some of the dying women. One woman who tried to protect her child had her fingers and other parts of her body slowly cut up.
That's an excerpt from the book WARSAW OF ASIA: THE RAPE OF MANILA. It has been dismissed though as “not well written.” Although I highly doubt if perfect scholarly work can hide the horrors of war. It's mostly the testimony of survivors.

50,000 thousand Filipinos died and the city, considered as one of Asia's most gracious then, was reduced to rubble.

The Philippines has 20 million Filipinos before the war. After the Japanese occupation, it was 1 million less.