One British person has been killed in India, after a series of attacks across the city of Mumbai.
At least 110 people have been killed, and around 300 injured in the attacks, which saw men with guns threaten people and take hostages.
The hostages are being held at two luxury hotels, and although some of them have been freed, no-one knows exactly what's going on.
Politicians have advised British people not to travel to India at the moment.
Prime Minister Gordon Brown said: "We will do whatever is necessary to protect British citizens and ensure the world is a safer place."
"This is a horrific incident which has shocked and outraged people around the world.
"We've got to do everything we can now to help the Indian authorities."
Police in India say the attacks were carried out by terrorists. A group called Deccan Mujahedeen, which experts know very little about, says it planned the attacks.
Many people, a lot of them from other countries, are being held hostage in the Oberoi Trident hotel.
Most guests have been brought out of the Taj Mahal hotel by soldiers, but police said some remained trapped.
A train station, hospital, and a restaurant popular with tourists, were caught up in the violence.
England's cricket team, which is in India, has postponed the final two one-day matches against India and is flying back home on Friday.
There is a Foreign Office emergency number if you're worried about friends or relatives. It's 0207 008 00 00