The Highways Department said a tandem wire on the Hong Kong-bound side of the Shenzhen Bay Bridge has snapped, but stressed the incident does not affect the safety of the structure.
During a meet-the-press session that was announced at short notice, the Director of Highways, Jimmy Chan, said officers found out about the snapped wire on Friday afternoon.
He stressed inspection and remedial works are now underway, and it will take around three weeks to replace the broken wire.
Two of the three lanes on the carriageway have to be closed off for the time being.
The Highways Department chief said initial investigation shows rusting may have caused the snap.
"We need to take samples of the broken part of the tandem to the laboratory for carrying out various tests, including the strength test and the metallic material test, so it will take a little bit of time before we can confirm the exact reason why there is rusting occurring at this part of the tandem", Chan said.
He added that authorities will inspect other bridges with similar design within three months to ensure their safety.