The Indian army is reportedly moving in on two hotels in Mumbai where terrorists have taken western hostages.
One of the Mumbai 'terrorist' gunmen, caught on Indian channel NDTV
Over 40 western hostages are reportedly being held at two luxury hotels in soutern Mumbai, say the Times of India.
A group calling itself the "Deccan Mujahedeen" has claimed responsibility for the attacks, according to the Press Trust of India.
Eyewitness reports say the attacks were aimed at British and American nationals.
At least 80 people have been killed and 250 are injured, say Mumbai police.
Gunmen have targeted several hotels, a popular tourist cafe and a crowded train station in at least eight attacks.
Attacks have been reported across southern Mumbai, at the Leopold Cafe, the Ville Parte, the Oberoi Hotel, the Trident Hotel, the Taj Mahal Palace Hotel, the Nariman House, the Colaba, the CST train station's Victoria terminus, JW Marriott hotel and one other location.
Map of the attacks in Mumbai
Guests at the Taj Mahal Palace hotel were said to be "terrified and trapped", according to reports from the Times of India.
The British Foreign and Commonwealth Office (FCO) is advising all Britons in Mumbai to stay indoors, after eyewitness accounts say the attacks are primarily aimed at western tourists.
Gordon Brown said: "These outrageous attacks in Mumbai will be met with a vigorous response.
"I have sent a message to Prime Minister (Manmohan) Singh that the UK stands solidly with his government as they respond, and to offer all necessary help.
"Urgent action is under way to offer every possible protection to British citizens in the region."
Mumbai on high alert after the spate of terror attacks
The White House has also condemned the attacks.
A spokesman said:"Our sympathies go out to the families and friends of those killed and injured, and to the people of Mumbai.
"We are monitoring the situation very closely and stand ready to support the Indian authorities as they deal with this horrific series of attacks.
"At this point, we are unaware of any American casualties."
Alex Chamberlain, a Briton caught in the attacks, said an attacker asked tourists if they were British or American before opening fire.
He added there was "no doubt in my mind" that the attacks were from a fundamentalist Islamic group.
The police commissioner A. N. Roy said: "These are terrorist strikes in at least seven places."
He added: "The terrorists have used automatic weapons and in some places grenades have been lobbed."
Tory MEP Witnessed Shootings
Conservative MEP Sajjad Karim was trapped in the Taj Palace Hotel in the southern part of the city as one of the attacks took place.
He told Sky News: "There was a lot of commotion in the main lobby, and then another gunman came right in front of us and started shooting.
"I saw a number of people go down, but I was fortunate enough to get away."
He added: "We've no idea what is going on outside."
Barry Moses, who lived in Mumbai for two years, told Sky News online the Taj Mahal hotel is the city's main luxury hotel, next to the Gates of India.
He added the restaurant Leopold's, which is "just around the corner" is popular with tourists and backpackers.
He said: "It's in all the books as a destination to go to. There will be very few Indians in there.
"I'm guessing, if anyone has been shot in the restaurant, they will include foreign nationals."
The Taj Mahal is where the English cricket team stay when they visit the city.
More follows...
Social Networking Bookmarks