One person has died and three have been seriously injured in a crash which has blocked the airport tunnel.

At about 5.40am, a car carrying five people was travelling northbound on General Holmes Drive when it crashed head-on with another vehicle.

A passenger in the northbound car died at the scene and three others have been seriously injured and taken to hospital.

#BREAKING: One person is dead, and two others are critically injured in Sydney after a crash in the airport tunnel heading south. #9News pic.twitter.com/oeO7w4GA4o

— Nine News Sydney (@9NewsSyd) February 5, 2020

The driver of the southbound car was the sole occupant and has been taken to St George Hospital for mandatory testing.

Crash Investigators are investigating how the head-on crash occurred and will address the media at midday.

All southbound lanes and one northbound lane of the Airport Tunnel were closed for several hours but have since reopened.

Traffic in the area remains “extremely heavy” with motorists advised to avoid the area and catch the train if possible.

MASCOT: 1 of 4 northbound lanes & all southbound lanes are closed on General Holmes Dr in the @SydneyAirport tunnel due to a 2-car crash. Southbound traffic on Southern Cross Dr can use the Airport exit, General Holmes Dr, Joyce Dr, Qantas Dr & Marsh St to join the M5 East. pic.twitter.com/URr8vYJ3tf

— Live Traffic Sydney (@LiveTrafficSyd) February 5, 2020