A tanker collided with a jetty in Milford Haven as it was attempting to dock in the early hours of the morning, causing damage to the vessel and berth.
Officials said the tanker suffered a "heavy berthing"
The incident happened next to the site of a liquefied natural gas (LNG) berth in the port.
The tanker was docking at SemLogistics - which stores oil-related products - when it suffered a "heavy berthing".
Port authority chief executive Ted Sangster said no-one was injured and a damage assessment was underway.
The tanker had been attempting to berth between midnight and 0100 GMT on Sunday.
An investigation into how the incident happened is being launched.
Mr Sangster told BBC Wales he did not know what the tanker was carrying but said there was no danger to the immediate area.
He said: "We're assessing what happened and an investigation will take place looking not just at the accident but what needed to be done.
"We will be looking at the cause of why it happened and what other steps can be taken to ensure that it doesn't happen again."
A spokesman for SemLogistics said "superficial" damage was caused to both the tanker and the jetty and that the vessel, the 18,000-tonne MV Prospero, was empty at the time.
There was no pollution caused and no-one was injured or evacuated, he added.
The Marine Accident Investigation Branch said they had been informed about the accident and were making some more enquiries before deciding whether to send an investigation team to the site.
The event occurred at No 2 SemLogistics berth, located next to the Dragon LNG berth which is used to import natural gas to two LNG terminals in Milford.
The terminals will link up with a 150-mile (241km) pipeline currently under construction between Milford and Gloucestershire which once completed will supply 20% of the UK's gas needs.
Some residents in Milford Haven formed a campaign group, Safe Haven, to try to prevent two LNG terminal being built in the town, citing concerns over safety.
However, their attempts were unsuccessful.
An offshoot campaign, Safe Haven Network, has also taken part in protests against the pipeline.