A man is currently climbing the Millennium Tower at 301 Mission (at Fremont). CBS 5's Joe Vazquez sent out this message: "'Skyscraperman' is climbing the Millenium Tower in San Francisco. He's halfway up."

Not sure why, exactly, the guy is heading up the 58-story highrise. We'll update as soon as we know more.

Update: Mission Street shut down between Fremont and Beale. Slew of firetrucks and cops lacing the area.

Update II: After three hours, Dan Goodwin, 54, reached the 58th-floor landing, where he was arrested. CBS 5 says Goodwin, a cancer survivor, "climbed the tower to draw attention to the vulnerability of skyscrapers to terrorist attacks and to raise awareness about cancer."