The fire caused evacuations at multiple buildings.
There is no word yet on any injuries or the cause of the blaze.
A cat was rescued and given oxygen and there may have been more inside. A man was seen in handcuffs at the scene, but police did not say why he was detained.
Calico cat rescued and given oxygen at #Hayward fire, she'll be OK pic.twitter.com/zP37YjTrMG
— Dean C. Smith (@DeanCSmith) January 21, 2015