By Michael Bristow
BBC News, Tiananmen Square
Journalists were prevented from wandering freely round the square
At first glance, it looked like any other day on Tiananmen Square this morning.
The square was full of people, including those on Chinese tour groups. They were easily identifiable by their identical baseball hats.
But a closer look revealed it was no ordinary day. The square was teeming with both uniformed and plainclothes security officials.
Police vehicles were parked on the square itself, and visitors had to go through airport-style security to get on to the open space.
Foreign journalists can usually wander freely around the square, but on 4 June most, including the BBC, could not.
Quickly moved on
There were blue skies over Tiananmen on the 20th anniversary of the massacre in which hundreds, if not thousands, were killed.
China's national flag fluttered alongside the Malaysian flag, in honour of a visit by the country's Prime Minister Najib Razak.
The square was not closed to the public - but China was taking no chances.
Uniformed officers from the Public Security Bureau and the People's Armed Police stood guard; there were just a few metres space between each one.
They appeared to be on high alert; they checked the credentials of suspicious looking vehicles driving around the square.
Security staff searched visitors' belongings near the square
An elderly woman sat on the ground was quickly moved on.
There were also hundreds, if not thousands, of what appeared to be plainclothes security officers.
Dressed casually and carrying water bottles, they scanned the crowds.
They all wore the same badge showing the Chinese flag and occasionally chatted with uniformed officers.
Many more sat outside the dozens of tourist buses that had brought them to the square.
I found out just how tight security was when I tried to get onto the central area of the square.
Chinese tourists and foreigners with passports were allowed through a security checkpoint where bags were searched - but I was not.
A police officer checked my passport, saw I was a journalist and told me that if I wanted to get on to the central area I would have to get permission from the Tiananmen District Management Committee.
I needed permission because I had a "special status", he told me.
I trudged off to the committee's office on the east side of the square. Once there, I was shown into a side room and given a bottle of mineral water.
"Drink up, it's very hot," said a polite official, who then promptly disappeared.
After about 15 minutes, another official returned and said I did not need special permission to go onto the square. "Just go through the checkpoint," he said.
I walked back to the square - this time to another checkpoint - and told the police officer what I had been told at the management office.
It made no difference. "He might say you don't need permission, but I say you do," said the police officer, quoting Beijing City Government order 203.
It was clear I was not going to be allowed on to the square on this sensitive day.