Sussex Police officers joined the South East Coast Ambulance Service in High Street.
An eyewitness described seeing a woman in distress, who was restrained by officers.
Traffic backed up in both directions, according to the witness.
Pictures from the scene show at least three police vehicles and two ambulances.
Sussex Police has confirmed officers were responding to an incident but could not give any detailed information yet.
. Shoreham High Street
Emergency services on the scene SUS-210313-121647001 Photo: eddie mitchell
1. Shoreham High Street
Emergency services on the scene SUS-210313-121437001 Photo: eddie mitchell
2. Shoreham High Street
Emergency services on the scene SUS-210313-121524001 Photo: eddie mitchell
3. Shoreham High Street
Emergency services on the scene SUS-210313-121605001 Photo: eddie mitchell
4. Shoreham High Street
Emergency services on the scene SUS-210313-121719001 Photo: eddie mitchell