The A27 is closed in both directions following a plane crash at the Shoreham Airshow.
The jet aircraft, a Hawker Hunter, crashed on the A27 about 1.20pm and the pilot is said to be recovering in hospital after being pulled from the wreckage.
Sussex Police said the plane hit several cars on the road just to the north of Shoreham Airport.
One section of the plane broke off, coming down in flames around 200 yards from the crash site.
There are unconfirmed reports of fatalities of several road users.
A police spokesman said: ‘The aircraft ended up in a bush.
‘There have been several casulties but we have no further information on these at the moment.’
Police advised drivers to avoid the A27 in the Shoreham area for rest of the day. The road is closed between Sompting and A283 Shoreham.
Visitors to the airshow have been told it may be ‘several hours’ before they will able to leave the area by road.
Vicky Stephens, 25, of Chichester, was on her way to Brighton when the crash happened.
She said: ‘I didn’t see the plane, just a sudden cloud of black smoke like a mushroom cloud, so I knew straight away that something had hit. Luckily I stopped for petrol first or I’d have been right underneath it.’
Eyewitness Stephen Jones told BBC News the plane was performing a loop and crashed before completing the the manoeuvre.
Mr Jones said: ‘The aeroplane involved is a Hawker Hunter T mark 7.
‘And he’d just begun his flying display.
‘He’d gone up into a loop and as he was coming out of the loop I just thought, you’re too low, you’re too low, pull up.
‘And he flew straight into the ground either on or very close to the A27, which runs past the airport.’
Shoreham Airshow has tweeted: ‘There has been a major incident outside the airfield boundary.
‘The emergency services are responding. Updates will follow when available.’
News of the accident has met with shock and concern for those involved.
One Twitter user, tweeting as @yunhollie, wrote: ‘I live in line with the runway at Shoreham airport, we saw the jet and it vanished. There was no bang, just smoke.’
User @Kimmychoo666 wrote: ‘My heart goes out to all those concerned at the Shoreham Air Show xx. I saw the black smoke, truly sad.’