UPDATED AT 10:16 P.M.
Services to Time Warner Cable customers affected by an earlier outage were restored earlier this evening, the TWS spokesperson told Patch.
However, no explanation of how a cable was cut had been offered as of late Sunday night.
UPDATED AT 3 P.M.
Less than 5,000 customers in all three cities were affected by Time Warner Cable outage Sunday, officials said.
A cut cable Sunday morning affected service to customers in Diamond Bar, Walnut and Rowland Heights, a Time Warner Cable spokesperson said.
The outage was reported about 3:30 a.m. Sunday, she said.
"Engineers have been working on this since early this morning, and we are currently estimating a few more hours before service will be fully restored," spokesperson Milinda Martin told Patch.
"We apologize to all affected customers, as we understand the inconvenience caused by loss of service," she added.
Martin said restoration of service was the company's "highest priority."
It was not immediately clear how many customers were affected altogether, nor how or where the cable was cut.