A problem with an underground cable caused a major power failure in Fall River, cutting off power to about 2,700 customers.

The problem was caused by a “technical fault” in an underground cable at National Grid’s Bates Street substation, just before 10 last night, according to Chris Mostyn, a spokesman for the utility company.

A fault, he said, occurs when there is a problem with the power distribution lines, such as an unstable connection or low voltage. When that occurs, a device similar to a home circuit breaker turns off the power to customers.

A Fall River police dispatcher said there was an explosion under a manhole cover on Quarry Street which he said was related to the power failure. But Mostyn, speaking from National Grid’s offices in Brooklyn, N.Y., said that local station controllers did not have any reports of an explosion.

“Until we get there and possibly speak to the police, we haven’t gotten any reports of an explosion,” he said.

By about 10:45 Wednesday night, Mostyn said the company had workers at the scene and had hoped to restore power to about half the affected customers within the hour, and get the remainder back online in the following few hours.

The company did not yet know the cause of the failure, he said.

tbarmann@projo.com