This is a type of DSC Alert and not a category, but is often found on many MF/HF radios as a specific type of Routine Alert. A Group alert is the Routine Alert sent on MMSI Group (MMSI begins with "0").

For example, a company representative from whom we rented the vessel for the flotilla cruise that we are on may contact all vessels in the flotilla.

After broadcasting the Group Alert on 2177 kHz, voice communication continues on the selected working channel.

Practise on the MF/HF radio simulator

Reception of a Group Alert

After receiving a Group Alert on DSC, the radio will automatically re-tune to the working channel. Then a voice message on the working channel should be listened to and voice communication could be continued.
On receiving a Group Alert you can either accept or reject the call.