(CNN) — Freedom of movement at the world's longest land border diminished on Wednesday when President Donald Trump announced restrictions on travel between the United States and Canada. "We will be, by mutual consent, temporarily closing our Northern Border with Canada to non-essential traffic. Trade will not be affected. Details to follow!" Trump tweeted. The decision will transform life at the northern US border with Canada, which nearly 200,000 people cross each day. And it's just one of a slew of travel restrictions appearing as world governments cope with the spreading coronavirus. Related content Hong Kong and Tokyo airports are handling coronavirus very differently. On Monday, the European Union announced it would close its borders to non-essential travel. In the UK, the Foreign Office has advised against all but essential international travel for a period of 30 days. In some cases, employers, organizations and even government agencies are limiting non-essential travel. On Wednesday, March 11, the US Department of State suspended non-essential travel by staff, with Reuters reporting an anonymous source saying individual decisions were being left to each respective US embassy, consulate and bureau. That leaves many wondering what qualifies as non-essential travel. The answer, it turns out, is not always straightforward or even easily enforceable. What it means on the US-Canada border Cars usually line up to cross into the US at the US/Canada border at Saint-Bernard-de-Lacolle, Quebec. DON EMMERT/AFP via Getty Images In a news briefing on March 18, a reporter asked President Trump to define non-essential travel between the United States and Canada. "Well I think essential is medical, we have military working together, we have industry working together, and again, it's not affecting trade, so things like that," said President Trump. "But just leisurely 'let's go to a restaurant and have dinner,' which a lot of people do ... we have ended on a temporary basis." Related content Travel and the coronavirus pandemic: Everything you need to know His reply underscored the lack of official clarity around the term. In Ottawa on the morning of March 18, Canadian Prime Minister Justin emphasized that both governments see supply chains as essential. "These supply chains ensure that food, fuel and lifesaving medicines reach people on both sides of the border," Trudeau said, noting that trucking would not be affected. The restriction, which Trump suggested could last 30 days, will prevent tourists from traveling between the two countries. "We're telling our citizens not to visit their neighbors if they don't absolutely have to," said Prime Minister Trudeau at his press conference. "These measures will last in place as long as we feel they need to last." Enforcement details are yet to be made public. Restrictions for the rest of the world European Commission President Ursula von der Leyen proposed that the EU close its borders to non-essential travel on March 16. KENZO TRIBOUILLARD/AFP/Getty Images The US Centers for Disease Control's Warning Level 3 , the agency's most severe advisory, now applies to Malaysia, Iran, China, South Korea, Europe, the UK and Ireland. In addition to warning against all cruise travel, that alert recommends Americans avoid all non-essential travel to listed countries, saying "the outbreak is of high risk to travelers and no precautions are available to protect against the identified increased risk." Despite the gravity of the advisory, the CDC still leaves it up to the individual to interpret what is, and what isn't, essential travel. And when it comes to restricting or recommending against non-essential travel, government decisions have varied widely. Related content Feeling overwhelmed? Top tips for staying positive online during the coronavirus crisis A March 17 press release by the UK government advising against all non-essential travel stated that "whether travel is essential or not is a personal decision." The Telegraph reports that it's the first time the Foreign and Commonwealth Office has made such a sweeping advisory. The European Union proposed stricter rules on non-essential travel across the external borders of the bloc, narrowly defining the exemptions. Only goods, medical equipment and some people working to manage the spread of the coronavirus will be allowed to enter the EU for a period of 30 days. In recent days, travelers have reported being turned back at the borders of the EU when their journeys were deemed non-essential. What is a lockdown? Some countries and regions are taking even more stringent measures, sometimes called "lockdowns" or "shelter-in-place." On Tuesday, March 17, the San Francisco Bay Area implemented an unprecedented public health order asking residents to stay at home except for essential needs. The order, which is in place through April 7, says residents may leave their homes to get food, care for friends and relatives, exercise, seek necessary health care and travel to essential jobs. Nearly 7 million residents are affected by the new rule, and government officials have announced that failure to comply with it is a misdemeanor offense. But there is currently no requirement of proof that you're allowed to be outside. It's the United States' first taste of the sweeping lockdowns that have been put in place in Italy, France and Spain. Related content What is and isn't allowed during a 'shelter-in-place' order As new coronavirus infections have slowed in China, Italy has become the new face of the epidemic. The entire country is under a total lockdown , with police patrolling streets to ask citizens if they have a valid reason to be out. As in San Francisco, valid reasons include food shopping, health reasons and work. When residents violate the order, they may face criminal charges. On Wednesday, The Guardian reported that Italy was charging nearly 40,000 people for violating lockdown. On Tuesday, France was also put into a lockdown . For a period of at least 15 days, anyone leaving the home must fill out and sign a paper explaining why they're out, with valid reasons including shopping for groceries and medicine, caring for family or getting to work when remote working is impossible. An exception is also made for the needs of pets. Rules can vary by city, region or country. Rules can vary by country It's not clear if New York City will issue a "shelter-in-place" order. John Lamparski/NurPhoto/Getty Images Spain is implementing serious restrictions as well, including closing land borders to everyone but Spanish citizens, residents and those citing force majeure. The country has declared a "state of alarm" f or an initial period of 15 days. During the state of alarm, individuals may only go out in public for a specified list of activities, including shopping for groceries or medicine, getting medical care, going to work, helping vulnerable people and going to financial institutions. Related content New York governor dismisses possibility of shelter in place order after mayor urged New Yorkers to prepare for it In the United States, it remains to be seen whether stringent shelter-in-place orders will become more widespread. After New York City Mayor Bill de Blasio suggested the city should be prepared for a possible shelter in place order, New York Governor Andrew Cuomo dismissed the idea , questioning the legality of such a ruling. He said all actions should be statewide, and called on Americans to remain calm in the face of coming disruptions. "This is an extraordinary time in this nation's history," he said. "It's a character test for us collectively as a society."