A special train carrying North Korean leader Kim Jong-un is traveling across China for a second summit between Kim and U.S. President Donald Trump in Vietnam. 

The train, which departed Pyongyang at around 5 p.m. on Saturday, was spotted passing through Tianjin in northern China on Sunday. 

Kim's train, running at 60 to 70 kilometers per hour, is expected to cross the Chinese border into Vietnam on Tuesday morning. 

Security has already been heightened in an area surrounding a train station on the border of China and Vietnam, with highways to Hanoi from the border area closed from 6 a.m. to 2 p.m. Tuesday.  

There was speculation that Kim may drop by in Beijing to meet with Chinese President Xi Jinping, but his train did not stop by the Chinese capital.