Gas explosion blows CBD manhole into air

A 50kg concrete and steel manhole cover has shot more than a metre into the air in an explosion under a Sydney CBD intersection, startling passing Christmas shoppers.

Smoke poured from the hole after the loud blast on Wednesday afternoon.

No one was hurt, but one passer-by said he was terrified by the unexpected explosion, especially in Australia's current security environment and after the recent Lindt Cafe siege.

An Ausgrid worker said the explosion happened because of a build-up of gas and an electrical fault.

It wasn't yet known if there'd been any damage inside the manhole, the energy company representative said.

However, it was possible the cover could be blown off again, although that was unlikely, the worker said.

A NSW Fire and Rescue service member said firefighters wouldn't enter the manhole until it had been checked by Ausgrid.

The manhole cover put back into its casing and normal traffic resumed.