Britain stands “shoulder to shoulder” with Japan as it faces an increased threat from North Korea, Theresa May told her counterpart as she arrived in Kyoto.
In a second day of talks on Thursday, the Prime Minister and Shinzo Abe will “explore” fresh sanctions against the rogue state, No 10 said.
Mrs May has called on China to step up its action against Pyongyang and refused to rule out British military action to stop its illegal weapons testing program.
But Beijing went on the offensive, with foreign ministry spokeswoman Hua Chunying claiming critics “only pay attention to sanctions and pressure, and ignore peace talks”.
She added: “You will reap what you sow. The parties directly concerned should take responsibility.”
Downing Street said the length of the time Mrs May and Mr Abe spent together on the first day of the three-day trip was “unusual” and showed the “strength and continuing positive relationship” between the pair.
The premiers met at the Omotesenke tea house in Kyoto, where the tea-making ceremony dates back to a man called Sen no Rikyu, the 16th century founder of the tradition.
Mrs May, wearing a red dress and white jacket – the colours of the Japanese flag – removed her trademark leopard print pumps before emerging at the back of the tea house side by side with Mr Abe, who pointed out the moss in the garden.
“Very attractive, very calm,” Mrs May said.
The leaders, flanked by interpreters, sat on a low bench behind the table while on the opposite side of the room, the master of ceremonies and his two assistants sat on the floor.
After a banquet that included “salted entrails of the sea cucumber”, Mrs May and Mr Abe boarded a high-speed bullet train to Tokyo.
Discussions over the course of the day focused on North Korea but also touched on Brexit.
Mrs May landed in Japan 36 hours after Pyongyang sent a missile over the northern Japanese island of Hokkaido, which landed in the Pacific Ocean.
A No 10 spokesman said: “The Prime Minister told Prime Minister Abe the UK stood shoulder to shoulder with Japan in the face of North Korean aggression.”