At least 42 people have died in South Korea, as the country grapples with a record heatwave with temperatures unseen in more than 100 years.

This is the highest number of deaths since South Korea began officially counting casualties due to heat in 2011. More than 3,400 people have been treated for heat-related illnesses, such as heat stroke, since the end of May, officials said.

Temperatures in the capital Seoul, which is home to about half the country’s population, reached 39.6 C last week, the hottest temperature in 111 years.

South Korea has been grappling with the extreme temperatures since late July, which have wreaked havoc on crops across the border in North Korea, a country that has often faced food shortages.

Most of the deaths were among elderly and poor people who lack air conditioning in their homes. But at least five died after working outdoors, including a man in his 30s and a migrant worker from Vietnam in his 50s.

The government has also said it plans to revise laws to include extreme heat as a form of natural disaster, allowing victims of heat-related deaths or illness to receive compensation.

The government has cut electricity prices for July and August in order to encourage citizens to use energy-intensive appliances like air conditioners. The cut is expected to save consumers about 267bn won (£186m), according to the ministry of trade, industry and energy.

The heat is also impacting the country’s military, in which all men must serve. A conventional ammunition depot exploded due to a “chemical reaction due to high-temperature heat”, the Korea Times reported, citing lawmakers. No one was injured in the explosion, but the magazine was near explosive materials.

The storage facility was built above ground rather than in an underground cave which is typically more secure.

“Concerning some of the storages in the middle of cities, the Army must immediately search all ammunition storages and check for any hazards possibly leading to accidents affecting citizens,” said opposition lawmaker Kim Joong-ro.

The heat has also led to some odd moments, such as when a chick hatched from a carton of eggs left on a balcony. The constant temperature of just below 40C meant there was no need for an incubator.