Indonesia and its neighbours are worried about the effects of the smoke, which has already been seen as far away as Thailand, and fear a return to the disastrous situation of 1997, local media reported.

Illegal land clearing in Sumatra’s jungle-clad province of Riau is believed to be the cause of the haze, according to Singapore’s The Straits Times . The newspaper quotes Mr Riyadi Usman, who heads a Sumatran environmental damage department as saying that “measuring equipment shows that the air over Pekanbaru in the past two or three days has reached the ‘unhealthy’ level in the mornings.”

The newspaper said that on 20 July, with visibility of less than 700 m at Sumatra’s main airport in the city of Medan, flights were suspended.

Usman told reporters that his office, local forestry officials and the provincial authorities were all co-ordinating efforts to prevent a repeat of the thick haze that blanketed the region in 1997, when choking particulates remained for several months causing extensive health and traffic problems in Indonesia, Singapore and Malaysia.

The Riau provincial administration, angered by the continuing forest fires, is reported to be demanding that Jakarta revoke for good the permits of errant companies responsible for the fires.

Action inspires action. Stay ahead of the curve with sustainability and energy newsletters from edie