A cable beneath 16th and Market Streets in Center City began smoking early this morning, causing officials worried about a separate gas leak to evacuate an apartment building.

The 10-story Oakwood Apartments building at 16th and Sansom was cleared of its residents, and 16th street was closed between Chestnut and Walnut Streets for much of the morning.

Karen Muldoon-Geus, a Peco spokeswoman, said the incident occurred about 3:30 a.m. when smoke was spotted coming from a manhole. Authorities initially believed the smoke was from a blown transformer, but later said it came from a cable.

"They're still assessing the situation but it had to do with a cable underground as opposed to a transformer," Muldoon-Geus said.

She said about 764 customers were knocked out of service for a few hours. At 3 p.m., 46 customers remained without power.

"We expect to have 30 of those back online by 5 and the remaining by 8 p.m.," she said.

"We're still assessing how the damage happened," she said.

Peco is coordinating with PGW and the fire department.

The apartments were ordered evacuated when reports of a gas leak came about the same time the underground fire was reported. The Red Cross of Southeastern Pennsylvania set up a center for evacuated residents at a nearby school and said it would help them find shelter for the night if necessary.