Last night seven people were killed in what the Metropolitan Police have described as a terrorist attack at London Bridge and Borough Market.
Some 48 people are being treated in hospitals following the attack, which the police say they responded to and stopped within 8 minutes.
Three attackers were shot dead at the scene.
When a terrorist attack is recent, there's a tendency for social media to inflate misinformation as people share details unchecked.
There's still many details yet to be confirmed by authorities about the attack.
Here's a brief guide to how to behave responsibly on social media at a time like this:
1. Get your news from official sources.
There have been incidents of people sharing false images claiming they are identifying attackers or victims.
You should receive details from official sources - by which we mean the relevant emergency services such as the Metropolitan Police, and statements from government figures such as the Prime Minister and the Home Secretary.
Don't believe all you read online.
Check your information is also confirmed by authorities, and if it's unconfirmed, just don't tweet it.
2. If you think you have information, send it through the right source before spreading it on social media.
Police are looking for information, photos and videos during crisis times.
If you are a witness at the scene or have seen footage of the incident, speak to police before sharing things online.
Sharing things online without going through the official channels, even with good intentions, can be a hindrance.
3. Don't share graphic images
You can distress others by showing photos of victims - indeed families of the victims could identify their relatives if you share images, before they are contacted by the authorities.
If you want to be helpful, share official police information instead.
4. Follow the advice of the authorities
The Police have issued advice for protocol during an incident.
They will also provide hotlines (not for general inquiry) and advice on how to behave online during an incident.