The company that constructed the California apartment building where six young Irish nationals died in a balcony collapse has paid millions of dollars in fines over other faulty balconies, the San Francisco Chronicle reports.

Court documents revealed that the firm, Segue Construction Inc., has paid $US6.5 million ($A8.4 million) since 2013 to settle two lawsuits over claims of balcony rot and failure, the paper said.

Dry rot and overcrowding could be responsible for the balcony collapse that sent the six tumbling to their deaths and injured seven others early in Berkeley.

There was a “high probability” that water had rotted the wooden slats supporting the balcony at the apartment complex, Berkeley Mayor Tom Bates said in the article, which appeared online on Wednesday.

Five Irish citizens and an Irish-American woman, all aged either 21 or 22, died when the balcony buckled at a building two blocks from the University of California campus in the city.

They were reportedly celebrating a 21st birthday party at the time of the accident.

The city of Berkeley, in a statement published online, ordered a second balcony removed from the building’s facade after deeming it “structurally unsafe.”

The municipality added that an official investigation is ongoing and that victims’ families continue to arrive in Berkeley from Ireland.

“There has been an outpouring of Berkeley community support for them,” the statement said.