A post on an online forum appeared to predict the terror attack at Westminster, according to internet users.

At least one man ran over members of the public with a car before trying to stab and injure police officers. He was shot by armed police next to the Houses of Parliament.

The attack may have been flagged by a post on the 4chan forum, which contained references to its exact location. It also contained a photo, taken from the internet, of two guns.

It isn't known that the post was anything to do with the attacker, and it made no explicit reference to the date or nature of the incident. But many internet users are pointing out the chilling coincidence of the two events.

The reference to the location was posted through a strange code. Alongside the picture, the user posted a series of dashes and dots – when translated into Morse code, they pointed to a URL, and at that page was the exact co-ordinates for the attack.

Video shows terrifying moment police open fire outside parliament

Those co-ordinates pointed to Westminster Bridge, which the attacker drove over. Specifically, they are located at the side where Parliament is located, which is where the shooting took place.

In pictures: Westminster attack Show all 9 1 /9 In pictures: Westminster attack In pictures: Westminster attack An air ambulance lands after gunfire sounds were heard close to the Palace of Westminster in London PA wire In pictures: Westminster attack MPs wait until the situation is under control in Westminster. 'The alleged assailant was shot by armed police,' David Lidington, leader of the House of Commons, told the house. BBC News In pictures: Westminster attack Crowds gather in Westminster after shooting incident, which police are treating as terror attack BBC News In pictures: Westminster attack Police were also called to an incident on Westminster Bridge nearby AP In pictures: Westminster attack Early reports indicate the car, which mounted the pavement on Westminster Bridge and mowed into around a dozen people, was the same vehicle which then rammed into the railings of the Palace of Westminster, just around the corner Reuters In pictures: Westminster attack Security sources described the suspected assailant as a middle-aged Asian man, who is understood to have left the car before attacking a police officer with a seven-to-eight inch knife PA wire In pictures: Westminster attack Police have asked people to avoid the immediate area to allow emergency services to deal with the ongoing incident AP In pictures: Westminster attack One woman has died and a number of others, including the police officer, have been hurt, according to a junior doctor at St Thomas' Hospital Reuters In pictures: Westminster attack At least three gun shots were heard by those inside Westminster, and proceedings in the House of Commons have been suspended AP

The post went live on the afternoon of 21 March, almost exactly 24 hours before the attack. It featured a note written on paint that included that date, making clear that it had been posted to 4chan's "Politically Incorrect" board.