UPDATE: The Sydney Harbour Tunnel has reopened following a power failure.
The power outage occurred just after 10.20am on Monday, diverting motorists to the Harbour Bridge.
The tunnel reopened just before midday.
Earlier On Triple M
The Sydney Harbour Tunnel is now closed in both directions.
A power failure has blocked the Sydney Harbour Tunnel.
The bridge remains open however traffic is very heavy as motorists already in the area are being diverted over the bridge.
Anyone needing to travel across the harbour is advised to use Victoria Road, Anzac Bridge or Ryde Bridge instead.
Traffic crews and utility crews are on site investigating the power failure as quickly as possible.
For the latest traffic information, visit www.livetraffic.com or call 132 701.
For the latest public transport information, visit www.transportnsw.info