Philippine traffic officers and crowd control personnel will wear adult nappies on the job during next week's visit of Pope Francis, when they will spend long hours marshalling crowds expected to run into the millions, authorities say.

The diapers will ensure about a thousand personnel can stay at their posts without diverting for the call of nature during the papal tour, Metro Manila Development Authority official Emerson Carlos said.

He said the diapers would get a trial run during the procession of the Black Nazarene, an annual parade of a wooden image of Jesus Christ that will also draw enormous crowds in the capital on Friday.

"We will be giving them these diapers because we don't know when the crowds may rush in," said Carlos, the agency's deputy general manager for operations.

The government expects millions from Asia's biggest Catholic population to turn out for the much-admired pope, especially for an early evening mass in Manila on January 18.

The nappy plan has attracted ridicule in Philippine media, but Carlos was undaunted.

"It just requires a shift in outlook if it is really necessary," he said, adding "there have been no complaints" from the traffic constables themselves.