A hole has appeared behind the end of the German wall at the eastern side of L'Ancresse, near the slipway.
The States of Guernsey has fenced the area off, and work will start next week to fill it.
Under the latest States resolution, Environment and Infrastructure are to keep repairing the crumbling World War Two defence work for a number of years.
A £150,000 repair plan was agreed in April.
Members of the public are being asked to avoid the area and not pass the barriers.
Protected status of Guernsey bunker changed by planners
The Planning Committee has reversed a decision made earlier this year is to give a bunker protected monument status.
Guernsey's former Chief Minister resigns as deputy after admitting making indecent images of children
Disgraced politician Jonathan Le Tocq has resigned from the States after pleading guilty in Guernsey's Royal Court to all 15 charges against him.
Guernsey Police seek Complaints Commissioners
The Police Complaints Commission is advertising for the role of Complaints Commissioner, following an ongoing review into the process.
200 knitted angels go to Guernsey hospital patients
Knitters from St Andrew’s parish have created more than 200 colourful knitted angels for patients at the PEH.
Woman dies after being found unconscious off Vazon Bay
A 39-year-old woman has died, police say, after all emergency services were called to Vazon Bay this morning.
Rotary Guernsey delivers its Christmas hampers
The charity is thanking islanders for giving £7,600 towards its Christmas Food Parcels appeal.
Le Tocq should resign as a Guernsey deputy says Lindsay de Sausmarez
Deputy Lindsay de Sausmarez says there is only one option to remove disgraced politician Jonathan Le Tocq, and that would be after his sentencing in late January.
L'Ecume II: Lewis Carr jailed for 20 months for fatal collision at sea
The former second officer in control of the Commodore Goodwill when it collided with a trawler, killing three fishermen, has been sentenced at Jersey's Royal Court.
