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SAN DIEGO — A small explosion caused by a malfunction in an underground transformer sent a manhole cover flying Friday, leading to a brief shelter-in-place order for residents and businesses in Liberty Station Friday, but there were no reports of any injuries.

The San Diego Fire-Rescue Department and San Diego Gas & Electric were dispatched to the area of Truxtun and Womble roads around 2 p.m., according to fire-rescue spokesman Jose Ysea. A witness told authorities that smoke was emanating from the sewer, but the smoke had dissipated within about 30 minutes, Ysea said.

A shelter-in-place order was issued for Liberty Station, which includes numerous supermarkets, shops, schools and homes.

Crews eventually determined the blast was caused by a blown underground transformer. After turning off electricity to nearby power lines, authorities determined the area was safe and lifted the shelter-in-place order.

“The only issue that remains is traffic,” Ysea said.

The Fire-Rescue Department asked people to avoid the area, since portions of the main thoroughfare Truxtrun Road were closed to allow crews to repair utility infrastructure.

A message sent to High Tech High parents read:

“Parents can access the school by using Womble Road and parking in the Trader Joe parking lot. School will end at the normal dismissal time.”