Dissident, now expatriate Chinese artist Ai Weiwei employs his celebrity to bring attention to the global refugee crisis in “Human Flow,” a documentary that’s as visual imposing as Ai’s art and, at nearly two-and-a-half hours, nearly as huge as the subject demands.

The director and his large crew (including a dozen cinematographers, including Ai himself) visit more than twenty countries to convey the magnitude of the crisis, both in terms of the estimated sixty-five million men, women and children fleeing war, famine and political repression, and of the many areas affected, from Africa and the Middle East to Asia.

While officials are allotted the opportunity to comment on the extent of the tragedy—for example, Princess Dana Firas discusses how Jordan has responded to the influx of Palestinians, Iraqis and Syrians, erstwhile Lebanese warlord Walid Jumblatt discusses the possibility of coexistence in Lebanon, and Palestinian spokeswoman Hanan Ashrawi speaks about the dehumanizing impact of refugee status, while United Nations representatives discuss the condition in overcrowded camps, or what awaits Afghans being sent home to an uncertain future after long living in Pakistan, or the Rohingya being forced out of Myanmar to Bangladesh—the emphasis is on the displaced. They are seen being rescued from boats in the Mediterranean and taken to Italian relocation centers, making semi-permanent homes in Jordanian camps, coming ashore on the Greek island of Lesbos, and trying to survive trapped in makeshift enclaves in eastern Europe or on the French coast, prevented from continuing the journey to Germany or England.

The stories they tell are, of course, heartbreaking. One man breaks down as he describes how nearly a third of the family members who were part of his group at the beginning have died in the attempt to reach safety, while others await the opening of gates that are likely to remain closed in Hungary and Macedonia (and are patrolled by army and police) or are effectively warehoused in a huge airport hangar in a comparatively welcoming Germany for processing.

Along the way we see Ai interacting with the refugees, commiserating with their plight and signaling his respect for them as a fellow displaced person, though one far better off than they. His artist’s eye is also in evidence, in images that are carefully composed and elegantly shot. Especially notable are the sequences of refugees marching in long lines under official supervision, and the shots taken from far above, from what might be called a divine perspective.

One could make the argument that “Human Flow” is sometimes too beautiful for its subject—that a grittier, less aesthetically pleasing approach might be more suitable. But Ai Weiwei’s artistry doesn’t obscure the size or urgency of the problem on which he focuses; he and his colleagues have done an extraordinary job of exploring the great human tragedy of our time.