Jubilant fans poured out onto the streets of Los Angeles Sunday to celebrate the Lakers' title-clinching win over the Orlando Magic in the NBA Finals. But it didn't take long for the crowds to turn unruly, forcing the LAPD to go on tactical alert.

About 25 people were arrested, most part of a rowdy crowd that split off on to surrounding streets after police declared the gathering an unlawful assembly, police officer Karen Rayner said. At least 18 people were arrested for disturbing the peace, arson and other infractions.

Crowds in the streets blocked traffic and rocked vehicles. Worried motorists ran red lights because they didn't want to stop at an intersection and be mobbed.

• Video: 18 people arrested in Lakers melees
• Video: Chief Bratton discusses wild celebrations
• Video: Deputies clear out unruly fans in East L.A.
• Video: Many fans hold peaceful celebrations