More than 1800 New Zealanders have registered as being safe and well in Japan where tens of thousands are feared dead after a magnitude 9.0 tremor followed by a tsunami devastated large areas in the north on Friday.

However, the Ministry of Foreign Affairs and Trade (Mfat) said it still had "specific concerns" about one New Zealander missing in the affected area.

Mfat had held concerns for Steven Brooking, a 37-year-old English language teacher who lived in the coastal city of Miyako, but he was safe and well, Mfat spokeswoman Catrina Williams told NZPA.

Mfat said 1815 New Zealanders in Japan had registered to advise they were safe.

Embassy staff were providing a range of consular assistance for those badly affected by the disaster, including visiting hospitals and evaluation centres.

Consular staff were also based at Narita International Airport in Tokyo and Sendai in the northeast to help.

Mfat has updated its travel advisory to recommend against all tourist and other non-essential travel to prefectures in Japan affected by the earthquake and tsunami, including Tokyo.

New Zealanders intending to travel to other parts of Japan were asked to email the ministry on cons@mfat.govt.nz to advise them of their wellbeing.

Meanwhile, New Zealand's Urban Search and Rescue (Usar) team in Japan have started work in the northeastern town of Minamisanriku in an effort to find any survivors.

The situation in the country has deteriorated, with explosions at the Fukushima nuclear facility resulting in a fire that is producing a cloud of life-threatening radiation.

A fresh fire has also broken out at a reactor at the power plant.

Radiation at four times a person's recommended level of safe exposure have been detected at the plant following the explosions.

Tokyo had reported slightly elevated radiation levels, but officials said the increase was too small to threaten the 39 million people in and around the capital.

France's ASN nuclear safety authority said the nuclear accident could now be classed as level six out of an international scale of one to seven.

Level seven has been used only once, for Chernobyl in Ukraine in 1986.

New Zealand Fire Service national manager of special operations and team leader Jim Stuart-Black said yesterday the team was "well aware" of the nuclear power plant issues emerging 130km south of their base.

"We have good information on the situation and are being kept well informed of all developments. We also have our own equipment and are constantly monitoring the atmosphere. The radiation levels here are the normal background levels."

Mr Stuart-Black said he, the Australian Usar taskforce leader and Japanese emergency officials were discussing their planned operations in the tsunami-affected areas and were about to carry out an aerial reconnaissance of the Minamisanriku area.

Minamisanriku, a coastal town about 90km northeast of Sendai, was one of the hardest hit areas by the tsunami, despite being several kilometres from the ocean. Officials have suggested that more than half of its 17,000 residents are missing.

Of all its buildings, only three have been left standing -a hospital, a wedding store and a school.

Police believe a train filled with commuters has been buried by debris from the tsunami.

The official death toll stands around 3300, but that is expected to rise.

- NZPA