The Chinese capital of Beijing is under a thick layer of toxic smog today.

Local authorities have issued a red alert and put an emergency response plan into action.

Factories have been ordered to close and half of all private cars have been taken off the streets.

It is the third time this month that extreme levels of pollution have been detected in the city's air.

BBC reports that the level of PM2.5 - representing the smallest and deadliest smog particles - in the Chinese capital could reach more than 20 times the level considered safe by the World Health Organization (WHO) over the next few days.