Police swarmed the Los Angeles Times building late on Friday after receiving a report of a gunman inside and have arrested one person, police said.
Reports that an unidentified person had threatened to open fire on the third floor of the building came in after 7 p.m. local time (0200 GMT), said Los Angeles Police Department spokesman Gus Villanueva. There were no reports of injuries or shots fired.
The Los Angeles Times newspaper, which has its headquarters in the building, said on social media website Twitter that a witness told one of its reporters a man "who allegedly made threats at Times building worked for a firm that rents space from the newspaper."
The newspaper also cited witnesses in reporting that the man said he had been depressed and did not mind killing and that he reportedly handed one person a bag of bullets.
Areas of the downtown office building were locked down by police who secured the perimeter and continued to search inside, Villanueva said.