Shipping and haulage firms have complained of "chaos" at Felixstowe Port in Suffolk, seeing goods directed away from the UK in the run-up to Christmas and the encroaching Brexit deadline.
The owner, Hutchison Ports, has blamed pre-Brexit stockpiling and the ongoing coronavirus pandemic restrictions.
"The imbalance in UK trade and Brexit stockpiling exacerbate current operational challenges and we are working with our customers and stakeholders to get through the current congestion", Hutchison ports said in a statement.
"Performance at the port remains under pressure due to the Covid pandemic, high levels of import traffic, the large number of empty containers and a large amount of unusually long-stay containers held at the port".
In an operational note posted to the company website, they said delays at Felixstowe would last "at least into December and possibly through into the New Year" - which could see widespread disruption for firms waiting for pre-Christmas deliveries.
Hutchison Ports UK recently brought back former boss Chris Lewis out of retirement to take up the role as chief executive for a second time, after he left the firm in 2010.
Speaking to the BBC on Saturday, freight manager Matt Hudson warned that continued chaos would lead to "increased shipping prices" that will be "passed on to consumers".
Mr Hudson, whose company is responsible for the distribution of cargo that arrives in Felixstowe, said containers were being left on the quayside because haulage companies were unable to acquire a time slot to enter the port.
"It's delaying freight going into shops for consumers to buy", he said. "Shops are struggling anyway at the moment because of the impact from the coronavirus".
"If retail outlets can't sell what is actually en-route at the moment in time for Christmas, potentially they could lose even more money than they have done already this year".
Citing "unacceptable" delays, one ship set to be unloaded at the port was redirected to Rotterdam last week.
Taiwanese shipping firm Evergreen ordered one of its ships to bypass Felixstowe due to "serious port congestion". Instead, the ship's haul was dropped off in Rotterdam before being ferried back to the UK through London's Thamesport.
A spokesman for the firm said they'd been informed by Felixstowe's owner that they would have to wait for up to 10 days before a berthing slot - where ships unload goods - became available.
"Such a delay is totally unacceptable," he said.
Trade representative Logistics UK, said that there has been a large increase in shipments currently entering the UK due to summer-time lockdown easing and increased stock orders from firms as the economy bounced back.
Businesses now have the added uncertainty of the encroaching Brexit deadline on 31 December, where the rules of the UK and EU's future trading relationship have not been finalised.
"We are worried about the situation but we understand the port are working on solutions now", said Logistics UK policy manager Zoe McLernon.
"With the end of the transition period coming, we've got to make sure that our ports can take the goods we need".
In September, former Transport Secretary Chris Grayling was hired to advise London-based Hutchison Ports Europe - the port's parent company. According to the register of MPs' financial interests, he receives a £100,000 wage for "around seven hours" of work each week.
During Brexit preparations, Chris Grayling was responsible for offering contracts to ferry firms that did not have any ferries.