Police are investigating an altercation in the Mermaid Quay area of Cardiff Bay,
Emergency services were called to a restaurant at around 8.20pm on Wednesday evening, amid allegations that a corrosive liquid had been thrown during the incident.
But according to police, it's believed the substance involved was not harmful.
Armed officers were spotted outside the Las iguanas restaurant in what was initially described as a serious incident.
A cordon was put in place with the public urged to avoid the area, but it has since been lifted.
South Wales Police are appealing for witnesses or anyone who was in Mermaid Quay at the time of the incident to come forward.
A spokesperson said: "We acknowledge the considerable public concern following this incident, however at this time, the liquid is not believed to be harmful."
"Officers would like to speak with anyone who was in the premises, or in the vicinity, between 8.15pm and 8.30pm who may have information that could assist their inquiries."
Anyone with information should contact South Wales Police on 101 or use the live web chat, quoting reference no. 2400378983.
Alternatively, contact Crimestoppers anonymously on 0800 555 111.
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