At the Empire State Building -- New York's tallest building again after three decades -- office workers nervously returned to work yesterday.

"Many people here are talking about leaving. There's a feeling that we're the only target still standing," said Assaf Shalev, chief operating officer of DiamondFloor.com, an Internet company on the 57th floor. Most offices reopened at the landmark building on Thursday, but many employees waited another day to return, still shaken by the terrorist attack that felled the twin 110-storey towers of the World Trade Center -- about 1½ kilometres south and 30 metres taller than the Empire State.

The Empire State Building has the dubious distinction of being the only other skyscraper in Manhattan to have been hit by a plane. On July 28, 1945, a B-25 bomber flying in fog crashed into the 79th floor, killing 14 people.

Building security was stepped up yesterday; only one entrance was open and guards checked identification. Metal detectors and bag searches have been standard at the Empire State since 1997, when a Palestinian gunman killed one sightseer and wounded six others before fatally shooting himself on the 86th-floor observation deck. A note found on his body suggested he wanted to "eliminate" his enemies, including Zionists.