Two shots heard from the direction of New Palace Yard, and a short, very angry burst of shouting.
Random noises are often heard from protesters in Parliament Square, but this sounded different.
From the press gallery windows, a few feet from my desk, two bodies were visible in the yard, on the cobbles between Westminster Hall and the exit to Parliament Square, both surrounded by police officers.
For the first few minutes, dozens of police officers ran in all directions in New Palace Yard, and it looked as if urgent medical attention was being administered to the two people on the ground. There were at least eight armed officers, some aiming their guns towards the road outside.
The gates to Parliament Square were closed, but were quite often opened to let police and medical staff pass in either direction.
There were early reports of casualties also on Westminster Bridge, but those of us stuck in the press gallery were in no position to confirm this.
At this stage, no one knew if the attack was continuing, or was over.
After quite a long time, a disembodied voice said out of the intercom in my office: “Attention. Due to a security incident, all buildings have been locked down. Please remain in your current position until further notice.”
Dozens of journalists are filing stories from the press gallery, but it is very difficult to tell from inside the building what is going on outside.
Some parliamentary staff are now being escorted by police across the corner of New Palace Yard, but it doesn’t look as if they are being allowed to leave the Palace of Westminster: more as if they are being moved to another part of the parliamentary estate.
A kind of joky humour, mingled with shock, prevails inside the building. Outside on the cobbles, a sheet covers what looks like a body.
For myself, I feel also a sense of anger that anyone should mount such an attack, met in the first instance by the admirable body of police officers who guard the Palace of Westminster.
The press gallery has now been evacuated, and Andrew hopes to file again later.