As Istanbul braces for a second wave of heavy snowfall, a total of 463 flights have been cancelled at Istanbul's Atatürk and Sabiha Gökçen Airports.

The number cancellations by Turkey's national flag carrier Turkish Airlines (THY) at Atatürk and Sahiba Gökçen International Airports were 327 as of Wednesday night. The airline said in a statement Wednesday that 327 of its flights on Jan. 26 and 27 were canceled due to the expected heavy snowfall across Istanbul.

Meanwhile, Turkey's biggest private airliner, Pegasus Airlines announced that 110 flights to and from Sabiha Gökçen airport had been cancelled preemptively due to bad weather conditions, also warning passengers of unexpected delays.

Turkish airline AtlasGlobal also cancelled 20 flights, whereas OnurAir said that six of its flights were cancelled so far.

All passengers were advised to check with their airlines for adjusted schedules or cancellations.

The General Directorate of State Airports Authority (DHMİ) had earlier announced that the number flights scheduled between 00.01 a.m. and 11.59 p.m. on Jan. 26 at Atatürk airport would be reduced due to heavy snowfall and storms. Sabiha Gökçen Airport also confirmed that it will reduce the number of aircraft able to take off and land each hour.

According to forecasts, the temperatures in Istanbul will drop by 7 degrees Celcius coupled with 60 km/h northeasterly winds. Heavy snowfall is expected to start around early Thursday, lasting for about four days in Istanbul and the surrounding area.

Experts warned that the snow depth will reach 20-25 cm in some areas as authorities urged citizens to be alert against icy roads and collapses in roofs of buildings.