[10] It was caused by forest fires resulting from slash-and-burn practices, principally on the Indonesian islands of Sumatra and Kalimantan, which then spread quickly in the dry season.

[32][33][34] Among the events disrupted or even cancelled due to the haze were the 2015 FINA Swimming World Cup in Singapore and the Kuala Lumpur Marathon in Malaysia.

Heavy rains in Sumatra and Kalimantan in the last days of October 2015 significantly reduced the size and number of fires, and improved the air quality in most affected areas.

[37] The agreement calls on Indonesia to take steps to solve the problem through its own efforts or through international co-operation, or else face legal action based on the impact of the haze on its south-east Asian neighbours.

[52] A duty forecaster at the Brunei Meteorological Department, Nurulinani Haji Jahari, said heavy thunderstorms would do little to relieve the hazy conditions because westerly winds were still expected to continue bringing more smoke from Kalimantan and Sumatra.

[21] In Riau's capital, Pekanbaru, authorities ordered the closing of schools to prevent pupils from being exposed to the haze,[33][59] and thousands were forced to flee the city.

Unhealthy Air Pollution Index (API) readings were recorded in 24 areas in the states of Sarawak, with Selangor and Langkawi in Kedah being the worst hit by the haze.

As a result, on 15 September, schools in the four states of Sarawak, Selangor, Negeri Sembilan and Malacca together with the Federal Territories of Kuala Lumpur and Putrajaya were ordered to close temporarily.

[78] On 4 October, as haze reached unhealthy levels in many parts of the country, the government announced that all states except for Kelantan, Sabah and Sarawak were to close schools again for two days.

Therefore, it was suspected, although not confirmed, that the haze was originating from Indonesian and not local sources, possibly as a result of monsoon winds blowing north-east from fires in Indonesia towards the direction of the central Philippines.

[100][101][102] On 25 September 2015, the government, for the first time, named five firms: Asia Pulp and Paper, Rimba Hutani Mas, Sebangun Bumi Andalas Wood Industries, Bumi Sriwijaya Sentosa and Wachyuni Mandira as responsible for the haze and instructed them to take measures to extinguish fires on their land, not to start new ones, and to submit action plans on how they would prevent future fires.

According to the southern unit of the Vietnamese National Centre for Hydro-Meteorological Forecasting, many provinces and cities in the Mekong Delta, such as Sóc Trăng, Cà Mau, Kiến Giang, Đồng Tháp, Bến Tre, and Cần Thơ also experienced similar foggy weather since the beginning of October.

[47] Residents were told to stay indoors as southern Vietnam saw a rising number of child patients suffering irritated eyes, nosebleeds, runny noses, and sneezing.

[124] Free face masks were distributed to residents in areas worst affected by the haze and many schools in Peninsular Malaysia, Sarawak, Singapore as well as Indonesia were ordered to close.

[127] Singapore launched legal action that could lead to massive fines against Indonesian companies blamed for farm and plantation fires spewing unhealthy levels of air pollution over the city-state.

[129] In Thailand, Songkhla Province governor Songpol Sawasditham set up a "war room" to provide aid to affected residents and to combat the impact of smog from Indonesian forest fires.

[40] Residents and non-governmental organisations in Riau and Central Kalimantan complained about the lack of aid and inaction from the Indonesian government over the ongoing forest fires.

[130][131] An NGO (non-governmental organisation) called the "Mandate of People's Suffering" as well as some Riau residents even wrote to the Malaysian government requesting aid.

Guam's Office of Homeland Security and Civil Defence spokesperson Jenna Gaminde warned the public to expect the haze to reduce visibility and adversely affect those with respiratory issues.

Western Melanesia was currently susceptible to winds from Typhoon Koppu and Champi pulling smoke plumes from vast fires in Indonesia and Papua New Guinea.

The World Resources Institute said in an October report that since early September, carbon emissions from the fires had exceeded average US daily output on 26 out of 44 days.

[142] Robert Field, a NASA scientist from Columbia University, stated: If the forecasts for a longer dry season hold, this suggests 2015 will rank among the most severe events on record.

[51]Weak enforcement of environmental laws have been criticised; in previous forest burnings, many of the perpetrators, who mostly comprised employees of Indonesian palm oil companies, had been caught with strong evidence of criminal activity but still managed to escape from getting heavier penalties.

[134][146] Indonesia – President Joko Widodo has instructed government agencies to revoke the permits of any palm oil companies involved in the burning of forests and urged the arrest of those responsible.

[149] While Indonesian Member of Parliament (MP) Hamdhani Mukhdar Said apologised to both Malaysia and Singapore over the haze,[150] Indonesia's Vice-President Jusuf Kalla restated his position that Indonesia has no obligation to apologise to neighbouring countries for the haze caused by "forest fires" lasting "a month at the most" when these countries were not "grateful" for the "months" of "fresh air from our green environment and our forests when there are no fires".

[154] October saw the Indonesian National Board for Disaster Management (BNPB) requesting help from Malaysia, Singapore or other countries to secure bigger aerial firefighting aircraft for Indonesia,[26] around the same time as the Indonesian cabinet finally agreed to receive international help with the crisis, with President Jokowi declaring that Indonesia was now "working with a number of countries including Singapore", and other officials saying that Russia had also offered to help.

According to Malaysian Minister of Natural Resources and Environment Wan Junaidi Tuanku Jaafar the MoU would let both countries "assisting and exchange ideas with each other in the case of jungle and peat soil fires while requiring Indonesia to comply with its side of the bargain".

[161] At first, Indonesia accepted the offers[162] but rejected it under a recent statement by its Environment and Forestry Minister as confirmed by its ministry's chief spokesman, Mr Eka Soegiri.

Thailand – Prime Minister Prayut Chan-o-cha ordered its Foreign Ministry co-operate closely with neighbouring countries to tackle the chronic problem that has gripped parts of Southeast Asia.

[144] The Thai government has also offered them help in tackling the haze problem according to its Foreign Ministry deputy permanent secretary Vitavas Srivihok, as the Indonesian envoy had admitted his country's efforts alone were not enough to stop the fires.