Foreign firms are evacuating staff from Japan, after fears of radiation leaks at the Fukushima Daiichi plant escalated further.
German car maker BMW and car part maker Continental are among companies moving employees out of the country.
Others, including software group SAP, are moving staff to southern cities within Japan.
Workers had temporarily suspended operations at the nuclear plant after a rise in radiation levels.
Radiation levels in Tokyo were higher than normal, officials said, but not at levels dangerous to humans.
The expatriate staff of international banks, including Morgan Stanley, BNP Paribas and Standard Chartered, have reportedly left the capital city.
However, the Japan-based International Bankers Association said that none of its members had ordered its employees to evacuate, and some financial firms were continuing "business as usual".
Although predominately staffed by Japanese employees, expatriates typically make up a large part of the management at the Tokyo offices of foreign financial firms.
Companies are moving to ensure the safety of their staff after an explosion and fire broke out at the Fukushima Daiichi power plant, about 220km north of the capital.
SAP said it would evacuate offices in Tokyo, Osaka and Nagoya. It said it had offered about 1,100 employees and their families transport and hotel rooms further south.
Private equity firm Blackstone is closing its office in Tokyo and relocating staff as well, according to the Bloomberg news agency.
A spokesperson for chipmaker Infineon said: "We've offered to move staff to the south but only a small amount have decided to go."
Many airlines operating through Tokyo have been affected, with dozens of flights to Japan halted or rerouted.
Deutsche Lufthansa said it was diverting flights away from Tokyo to Osaka and Nagoya, while Air China cancelled flights to the Japanese capital from Beijing and Shanghai.
At Hong Kong's international airport, many passengers arriving from Tokyo said they were relieved to have left.
Cindy Khemalaap and her husband had been due to relocate to Hong Kong from Tokyo later this month, but decided to bring forward the move because of their fears about radiation and worsening food and fuel shortages.
The US citizens had been living in Tokyo for five years, and they had to leave their dog behind.
"We just took what was necessary. My husband will have to go back at some point and sort out the rest of our belongings," she said.
"We didn't sleep all last night. There were more aftershocks."
Japanese housewife Miyuki Yoshimoto shed tears when was greeted by her husband, who works in Hong Kong. She was taking a trip home to Tokyo with her five-year-old daughter and two-year-old son when the quake struck.
"I was very scared," she said. "And people are beginning to panic."
But other arrivals from Japan stressed that businesses were operating normally in parts of the country less affected the earthquake.
Martin Barrow, a London based businessman who was in Osaka when the earthquake struck, said he had managed to attend all his meetings in the country and was in Hong Kong as scheduled to complete his trip.