Protocol-conscious Japanese were on faux pas alert Thursday with Philippine President Rodrigo Duterte due to meet Emperor Akihito, the nation's most revered figure.

Duterte, who has made a habit of hurling sharp, even profane, insults at world figures, is on his first visit as president to Japan, a nation perhaps known more than any other for politeness and strict codes of conduct.

Concerns about Duterte's behaviour during his trip spiked after a video of him in China last week meeting with President Xi Jinping showed him apparently chewing gum -- considered rude in Japan for such an occasion.

He was also seen standing at the event with his hands in his pockets, another no-no.

Since arriving in Tokyo on Tuesday, Duterte has avoided any major trouble, though he has kept up a barrage of insults against Washington. Still, a summit meeting with Prime Minister Shinzo Abe on Wednesday went off without a hitch.

But as the trip approaches its end, the tough-talking former mayor of Davao, who has launched a violent and deadly crackdown on crime, is due to meet 82-year-old Emperor Akihito on Thursday.

Some Japanese are worried Duterte will offend the deeply respected figurehead.

Japan's emperors were once worshipped as living demigods and the throne is still venerated by much of the public, despite being largely stripped of its mystique and quasi-divine status in the aftermath of World War II.

Most Japanese bow when meeting the emperor, though foreigners generally shake his hand.

"Why did you put your hands in your pockets and chew gum in front of President Xi Jinping?" asked Kunihiko Miyake, a former diplomat, in a column published in the conservative Sankei Shimbun on Thursday.

"Some see them as simple rudeness but I suspect these are also performances," he added, noting Duterte's privileged upbringing -- his father was a lawyer and his mother a teacher -- while the president himself is a one-time prosecutor.

Former defence minister Itsunori Onodera said on Fuji TV on Sunday that how Duterte behaves when meeting Akihito could even impact on the two countries' relationship.

"I hope the Philippine side will remind him of that point," Onodera said.

Social media users also expressed concern.

"Is it going to be alright?," one Twitter user wondered. "I hope he won't chew gum like he did in China."

"Duterte, I beg you, please behave well at least in front of the emperor," said another Twitter post.

But Seiichi Igarashi, associate professor of international politics at Chiba University, said Duterte was unlikely to be rude.

"It's hard to predict what he's going to say... But he says he's pro-Japanese and he hasn't made any hostile remarks against Japan," Igarashi told AFP.