At least four people were injured in a six-alarm fire that ravaged a 4-story apartment complex in Redwood City, Calif., Thursday morning, authorities said. One of those injured is in serious condition, the San Francisco Chronicle reported. The blaze at the 74-unit apartment building was reported to the Redwood City Fire Department at about 5:30 a.m., KNTV, San Jose, Calif., reported. Several roads were shut down to give firefighters access to the fire. The cause of the fire is under investigation.