JAKARTA - Indonesian President Susilo Bambang Yudhoyono has apologised to Singapore and Malaysia over fires that have cloaked the countries in thick haze, as thousands more emergency workers were deployed Tuesday to tackle the blazes.

Southeast Asia's worst smog crisis for years pushed haze levels in Singapore to a record high last week, with residential buildings and skyscrapers shrouded and daily life for millions in the city-state dramatically affected.

The smog has drifted north and is now badly affecting Malaysia, while in a badly-hit province on Indonesia's Sumatra island - where the fires are raging in peatland - hundreds gathered to pray for rain.

The crisis has triggered a war of words between Jakarta and its neighbours, with an Indonesian minister accusing Singapore of acting "like a child". But Yudhoyono sought to ease tensions by issuing a public apology late Monday.

"As the president of Indonesia, I apologise for what has happened and ask for the understanding of the people of Malaysia and Singapore," he said. "We accept it is our responsibility to tackle the problem."

Singapore and Malaysia have been pressing Indonesia to step up action to fight the blazes but Jakarta has hit back, insisting some fires are in plantations owned by companies from its neighbours.

However, Malaysian Prime Minister Najib Razak said the question of who owns the plantations "is not the issue here", national news agency Bernama reported.

"There should be no concern about whether the plantations are owned by Indonesia, Malaysia or Singapore but rather action should be taken against those responsible," he said. Najib said he had sent Yudhoyono a letter demanding Jakarta act to punish those who had caused the fires.

Police in Riau province, where the fires are centred, said they had arrested nine people so far on suspicion of starting the blazes, all small palm oil farmers. Smog from Sumatra is a recurring problem during the June-September dry season, when big companies and smallholders alike light fires to clear land, in a cheap but illegal method of clearing space for planting.

Southeast Asia suffered its worst smog outbreak in 1997-98, which cost the region an estimated $9 billion, and was hit with a serious recurrence in 2006.

Indonesia's national disaster agency said Tuesday that more than 3,000 emergency workers would be sent over the next two days to Riau to join some 2,300 already tackling the blazes.

Firefighters are backed by helicopters and planes dropping water and attempting to chemically induce rain through cloud-seeding but agency official Agus Wibowo said the airborne efforts were proving ineffective.

The agency was shifting its focus to "sending more men to the affected areas to fight the blazes on land", he told AFP. The blazes are difficult to tackle as they are burning under the surface of the peat.

While the smog has lifted from Singapore, which was enjoying its third straight sunny day on Tuesday after the air pollution index eased from the all-time highs of last week, Malaysia is now bearing the brunt of the crisis.

Air quality was "hazardous" in two Malaysian districts, including the country's busiest port, Port Klang on the Strait of Malacca facing Sumatra, where the readings stood at 484 mid-morning Tuesday.

Readings above 300 indicate "hazardous" conditions. Three other areas, mostly in central Malaysia near the capital Kuala Lumpur, logged "very unhealthy" air quality.

In one Riau district almost 300 people were evacuated over the past two days as fires raged close to their houses, some of which were burnt down, police said.

In Dumai city in Riau, where visibility has deteriorated to just 150 to 200 metres (500 feet to 650 feet) and residents have been advised to limit outdoor activities, hundreds gathered to perform special prayers calling for rain.

"This morning, we prayed to God for rain and for the efforts to fight the haze to be successful," said local environment official Basri, who like many Indonesians goes by one name.