The Indonesian government yesterday vowed to impose criminal charges on companies, as the authorities sealed off more plantations run by a further 13 companies amid worsening haze in the region.

On Friday, the authorities suspended plantations owned by 29 companies, including subsidiaries of four Malaysian groups and an Indonesian company owned by a Singapore-based group.

The additional plantations bring the total area of plantations suspended to more than 6,000ha, Indonesia's Environment and Forestry Ministry said.

Sealing off means the plantations cannot operate while an investigation is carried out by the authorities.

Under Indonesian criminal law, the courts can impose punishments including jail terms for company executives, fines and seizure of corporate profits, the ministry's director general for law enforcement Rasio Ridho Sani said in a press conference yesterday.

"The government has a serious commitment to prosecute (these companies). We will be able to address the fires only if we can change the behaviour of the people and the companies, and we will take strict measures to do that," he said.

In 2015, large parts of Indonesia and the surrounding region were smothered by choking haze for over a month. South-east Asia's largest economy suffered losses of about US$16.1 billion (S$22.1 billion), according to the National Disaster Management Agency (BNPB). About 500,000 people suffered respiratory illnesses.

Mr Rasio said the government could order convicted companies to pay compensation for the damage as well as impose administrative sanctions, including revoking operational permits.

Indonesia, home to the world's third-biggest tropical rainforest, is struggling to curb fires engulfing Sumatra and Kalimantan as it faces a longer-than-usual dry season this year. From January to August, burnt areas totalled 328,724ha, of which 27.3 per cent were peatlands, according to BNPB.

Peat fires are harder to put out because they can keep burning underground for weeks, especially in deep peat areas. Peat fires also produce thick, acrid haze.

The BNPB has deployed 9,072 personnel to fight fires across fire-prone areas, used 42 helicopters for water bombing and carried out cloud seeding to try to induce rain.

Despite the concerted efforts, the haze has spread to Malaysia and Singapore, triggering a diplomatic row between Kuala Lumpur and Jakarta.

Among the companies whose plantations were sealed off by the Indonesian authorities were four subsidiaries of Malaysian groups - Sime Darby, IOI Corporation, Kuala Lumpur Kepong (KLK) and TDM - and one Indonesian company, Sampoerna Agro, owned by Singapore-based Sampoerna Agri Resources.

Part of the investigation is to find out who was in charge at the time of the alleged fires, Mr Rasio said.

Malaysia said it is leaving it to Indonesia to investigate and prosecute companies accused of fires on their concessions.