China said on Tuesday it was "very concerned" about the safety of its citizens in Japan as it announced plans to evacuate Chinese from the quake-hit nation's disaster zone.

"The (Communist) party and state leaders are very concerned about the safety of Chinese nationals in Japan," ministry spokeswoman Jiang Yu told reporters.

Jiang spoke after the Chinese embassy in Japan began an operation to help its citizens get out of danger areas and return home to China as fears mounted over radiation leaks from a stricken nuclear plant.

The embassy in Tokyo issued an urgent notice, saying it was sending buses to four areas in Japan including Miyagi and Fukushima -- where the damaged nuclear power station is located.

"Our embassy has sent working groups to affected areas coordinating with the Japanese side to help the evacuation work," Jiang said.

The Chinese consulate in Niigata on the western coast said 20 buses had been sent to pick up 900 people after last Friday's 9.0-magnitude earthquake and resulting devastating tsunami, which have killed more than 2,400 people so far.

There are about 33,000 Chinese nationals living in five disaster-hit Japanese prefectures, the official China News Service said.

"As of now we have received no reports of Chinese casualties but we will continue to closely follow the situation and spare no effort in providing assistance and help to Chinese nationals in Japan," Jiang said.

According to a Chinese media report, air tickets from Japan back to China are in hot demand since the disaster, and some passengers were spending up to 200,000 yen ($2,400) for touted tickets.

Japan's nuclear crisis escalated on Tuesday as two more explosions and a fire rocked the quake-stricken Fukushima No. 1 atomic power plant, sending radiation up to dangerous levels before authorities said they later fell.

Authorities in Tokyo detected a higher than normal level of radiation in the Japanese capital, which is some 250 kilometres (155 miles) southwest of the troubled facility, which also fell later.

Jiang said no abnormal levels of radiation had so far been found in China, and that all of its own nuclear facilities were "functioning normally."