Lightning strikes have killed an unprecedented 59 people in Bangladesh in three days as tropical thunderstorms hit the country before the annual monsoon, an official said Sunday.

Thirty-four people were killed on Thursday in different locations and another 25 over the next two days around the country, disaster management department chief Reaz Ahmed told AFP.

"We've not seen such a huge number of deaths due to lightning before," Ahmed said, adding most of the victims were farmers struck while working in their rice paddy fields.

Lightning in the course of tropical storms usually strikes Bangladesh during the pre-monsoon and the monsoon season, which runs from June to September.

According to the disaster management department, 200 people have died on average every year from lightning strikes since 2011.

Weather expert Shah Alam said deforestation was to blame for the increased number of deaths, especially the cutting down of taller trees like palms that used to attract lightning bolts.

Alam, a former head of the Bangladesh Meteorological Department, said farmers and other labourers were also carrying more metal objects such as cellphones than before. Many were also working through the storms rather than traditionally waiting until they had passed.

Authorities said they plan to launch an awareness campaign from Monday on the dangers.

"We'll ask the people not to work in open spaces such as farmland, avoid the use of electronic gadgets such as mobile phones and not to stand under metal electric poles or big trees during lightning," Ahmed said.

Ahmed said authorities would also conduct research to determine whether the ferocity of the lightning storms was linked to warmer temperatures from climate change.

The meteorological department has already trained 20,000 school students on preventive measures during lightning.