However, evacuation is not necessary, Hoang Van Thuc, deputy head of the Vietnam Environment Administration, told VnExpress Thursday.

He said the mercury level in the air within a 200 m radius of the warehouse's fences was recorded on August 31 at over 10 nanograms per cubic meter.

The World Health Organization deems mercury levels from 5 to 10 nanograms per cubic meter to be safe, he added.

While residents within a 500 m radius of the warehouse's fences could have their health affected by mercury exposure, it was not serious enough to warrant an evacuation, Thuc said.

He said the residents in these areas should wear masks and long-sleeved clothing whenever they get near the scene of the fire.

People within the 500 m radius can get free health checks from the municipal Department of Health, Nguyen Duc Chung, Chairman of the Hanoi People’s Committee, said Thursday.

Chung also said Hanoi police should seek assistance from the Vietnam Academy of Science and Technology and other independent parties with sufficient capacity to perform further tests to compare with current results.

The Rang Dong company will be responsible for dealing with pollution in the area of the fire, and would have to provide authorities with information on the origins of mercury stored in its warehouse, as well as other documents relevant to its storage, Chung added.

A five-hour blaze that started at 6 p.m. on August 28 destroyed a third of the inventory at the 6,000-square-meter warehouse belonging to the Rang Dong company in Thanh Xuan Trung Ward in the southwestern Thanh Xuan District. The inventory included thousands of light bulbs.

Initial investigations show that the cause of the fire stemmed from storage procedures and there was "no sign of sabotage," Chung said. The exact cause is yet to be determined.

Rang Dong had reported that over 15 kilograms of mercury were released into the atmosphere by the fire, but scientists estimate the actual figure could be over 27 kilograms, the Ministry of Natural Resources and Environment said at a press conference Wednesday.

"The Rang Dong fire has inflicted big damage on assets and has had negative effects on nearby residents and the environment," Deputy Minister of Natural Resources and Environment Vo Tuan Nhan said at the conference.

Residents near the fire in the following day started moving out of their homes due to health concerns. Several reported fatigue and stinging eyes.

Rang Dong, a leading manufacturer of lighting products and equipment, has estimated loss from the fire at VN150 billion ($6.4 million).