Heavy snowfall has swept northwestern Turkey, grounding hundreds of flights, disrupting ground transport and closing schools in Istanbul.

Turkish Airlines announced the cancellation of 250 international and domestic flights to and from Istanbul's Ataturk and Sabiha Gokcen airports on Monday.

The airline also canceled at least 149 flights scheduled for Tuesday.

The snow began Sunday evening and is expected to continue until Tuesday night, according to Turkey's General Directorate of Meteorology, which also warned of heavy rainfall and a risk of flooding in southern Turkey.

The governor of Istanbul, Vasip Sahin, said on Twitter that schools would remain closed on Monday. Rough sea conditions also disrupted ferry services.

A cold snap in Istanbul over the New Year left thousands of passengers stranded, but temperatures had been milder recently.