LONDON — At the ports and terminals on Britain’s southeastern coast, a new era began on Friday morning without much fuss. Ferries and trains that carry goods to France from Dover and Folkestone were running on time, and drivers snaked their trucks into the port unencumbered by congestion.

To all appearances, little may have changed on Jan. 1, the country’s first day outside the European Union’s single market and customs union. It was, after all, a public holiday and not much business was taking place.

But for the first time in over 25 years, goods traveling between Britain and the European Union will no longer move freely and customs checks will be enforced for goods entering the bloc.

A trade deal, signed into law in Britain in the early hours of Thursday, less than 24 hours before it took effect, means the country and the European Union will trade goods without tariffs. Businesses, however, will still face significant changes that they had been urged to prepare for even during the lockdowns, closures and other social restrictions that the government has introduced to contain a surging coronavirus pandemic.

The changes are bound to bring “bumpy moments,” a top cabinet minister predicted this week. The government expects new customs paperwork alone to cost British businesses 7 billion pounds (about $9.6 billion) a year. The European Union is Britain’s largest trading partner, with £670 billion of imports and exports, and Britain imports far more goods from the bloc than it exports. (It has a trade surplus in services, which aren’t covered by the trade deal.)

Britain has at least 150,000 exporters who have never sent their goods beyond the bloc, according to data from the country’s tax agency, and will therefore need to make customs declarations for the first time. Border checks within the European Union were scrapped in 1993.

This is a change that will be immediately felt at Britain’s ports, especially the busy Port of Dover and the Eurotunnel terminus at Folkestone, which connect the country to France. But on Friday, with most business halted for New Year’s Day, trains and ferries were reported to be running smoothly. Eurotunnel reported that 200 trucks had used its shuttle train by 8 a.m., with all the correct documents.

“It does seem pretty calm,” Elizabeth De Jong, the policy director of Logistics U.K., a trade group, told Sky News on Friday morning.

But she added that businesses now faced “a new, different language of customs arrangements” that would need to be understood. She described the next few weeks as a live trial, as companies must ensure they have the correct paperwork for themselves and the goods onboard, and traffic has to be managed into the area.

Away from the Dover-Calais crossing, there were some early hiccups.

Six trucks bound for Ireland, a member of the European Union, were turned away from boarding a ferry at Holyhead, a port in Wales, according to Stena Line, a ferry operator. The drivers did not have the authorization now required for trucks crossing from Britain into Ireland — in this case, a digital “pre-boarding notification,” from Ireland’s tax bureau.

The ferry company, sensing an opportunity in Brexit’s potential headaches, has increased the number of direct sailings it offers between Ireland and France, bypassing Britain and the need for customs checks.

In what the British government has described as a worst-case scenario, 40 to 70 percent of trucks heading to the European Union might not be ready for the new border checks. This could lead to lines of up to 7,000 trucks heading to the border and delays of up to two days, according to a government report.

Britain has only recently cleared a huge backlog of trucks from the border. Late on Dec. 20, the French government suddenly closed its border for 48 hours to stop the spread of a new coronavirus variant from England. Thousands of trucks and their drivers were stranded for days. Once the border reopened, the drivers were then required to show a negative coronavirus test result before being allowed to enter France.

The delays at the normally fast-moving port also raised concerns about Britain’s supply of fresh food, much of which is imported from the rest of Europe in the winter. One fruit supplier urgently arranged to fly goods into the country, and British exporters of fish and shellfish scrambled to send their goods into France before they spoiled.

The spectacle amplified concerns about trade after Dec. 31, the end of the Brexit transition period. Even though goods are already moving more slowly because drivers’ coronavirus tests can take about 40 minutes to deliver results, it is unlikely that trucks will be waiting in their thousands to enter France on Friday thanks to the quieter holiday period.

In fact, some ferry crossings between Dover and Calais were canceled on Friday afternoon because demand was so low.

“We would expect sustained disruption to worsen over the first two weeks as freight demand builds,” the government report says. This could last about three months.

Frictionless trade has been replaced by a myriad of electronic and paper declarations for exporters, importers and logistics companies. Goods entering the European Union from England, Scotland and Wales now require customs checks, including safety certificates, and truck drivers will need a permit to enter Kent, the county containing Dover and Folkestone, to confirm that they have the necessary documents.

Truck drivers coming the other way face fewer requirements for now. Britain has relaxed the rules for goods arriving into the country from the European Union for six months.

In Calais, the first vehicle to depart for Britain via the Eurotunnel shuttle train on Friday morning was from Romania, carrying mail and parcels. The mayor of the French coastal city, Natacha Bouchart, pushed a button allowing the truck to leave.

It was a “historic moment,” she said, that “will have consequences whose range we don’t yet know.”

Antonella Francini contributed reporting from Paris.