Vegetables, fruits and meat sold there must not be consumed for the next 21 days, the Ha Dinh Ward People’s Committee stated in a release.

Dust and other contaminants from the fire have already affected the health of people in the ward, which sits next to Thanh Xuan Trung Ward where the Rang Dong Light Source and Vacuum Flask Joint Stock Company is situated, Tran Thi Nhien, deputy chairwoman of the committee, said.

Vegetables and fruits grown within a 500m radius of the fire must be destroyed, and children and sick and senior people need to be evacuated for 1-10 days, the committee warned.

Anyone with symptoms like coughing, chest pain or sudden fever must be taken to hospital promptly, it noted.

Clothes contaminated by the dust released by the fire must be cleansed with soap and bleach and rinsed thoroughly with water, it added.

Mercury risk

Nguyen Ngoc Tho, 42, whose family lives in an apartment in Ha Dinh about 150m from the burned warehouse, said: "Since morning I’ve been dizzy and my head hurts. Every time a wind blows, I find it hard to breathe."

They have tried to seal their doors and windows since Thursday night, but the charred smell still lingers, he added.

Tran Hong Con of the chemistry department at the Vietnam National University-Hanoi, said light bulbs contain glass, plastic and mercury, and when burned the plastic, mercury and fluorescent powders may be broken down and released into the air, causing symptoms like headache and chest pain if inhaled, he added.

Mercury in particular is a toxic metal which accumulates in the human body and is hard to get rid of, he said. High levels of mercury could cause many dangerous complications, including anemia, he said.

"A few burned light bulbs is not a problem, but if tens of thousands of them burn at the same time, there will be a definite impact. I believe there needs to be an inspection soon to find out the number of burned light bulbs and how much mercury they contained so that people could be reassured."

A five-hour fire destroyed a third of the stocks in the 6,000-square-meter warehouse in Thanh Xuan District, including many light bulbs.

The company estimated the loss at VN150 billion ($6.4 million).