The thick haze has forced four airlines to cancel 21 flights at the Senai International Airport early this morning.

Senai Airport Terminal Services Sdn Bhd's chief operating officer, Noor Safura Suib said the cancellations were due to low visibility of less than 1,000 metres from 6 am to 8.30 am.

"All the flights involved domestic and international routes with passengers affected totalling 1,000," she said when contacted by Bernama today.

Noor Safura said at noon five flights, namely two Malindo, a Firefly, an AirAsia and a Malaysia Airlines Berhad each were, however, allowed to take off after conditions improved.

The Air Pollutant Index (API) in the Pasir Gudang region recorded a very unhealthy reading of 201 as at 9 am, but it was down to 180 as at 3 pm today.

The Larkin Lama area also experienced severe haze with an API reading of 172 and Kota Tinggi (123) at 3pm.