ATHENS, Greece—An explosion left three people injured and seriously damaged an office building while shattering nearby storefronts in a busy part of central Athens early Wednesday. Fire department officials said a 77-year-old man was hospitalized with burns. Two others received medical attention for smoke inhalation. The pre-dawn blast occurred 200 meters from the ancient Temple of Olympian Zeus on the busy Syngrou Avenue. Firefighters were using aerial ladders to look for anyone possibly trapped inside the damaged buildings. As dawn broke, they forced their way into damaged stores to free several people trapped inside. The cause of the blast wasn’t immediately clear.