There are reports of attacks at seven locations
UK nationals have been offered assistance to leave Mumbai by the Foreign and Commonwealth Office.
Shootings across the Indian city were condemned as "an attack on all of us" by Foreign Secretary David Miliband.
Gunmen targeted at least seven sites late on Wednesday, killing at least 119 people and injuring 300.
A reception centre has been opened, transport and accommodation has been laid on and consular staff will be on hand at Mumbai airport.
Mr Miliband expressed his sympathy with the family of the one Briton who has been confirmed dead.
He said: "This is a callous, inhuman and indiscriminate attack on people of all races and all religions.
"This attack in Mumbai is an attack on all of us because democracy in India is vibrant and because Mumbai is one of the world's most diverse cities.
"The most terrible thing is that we do have one confirmed British fatality. Obviously our hearts go out to the family of the victim and we are determined to do all we can to support those who are currently in hospital."
British nationals requiring assistance in Mumbai have been advised to contact the British Emergency Centre in New Delhi on +91 1124192288.
The Foreign Office says it has been taking steps to assist UK nationals caught up in the turmoil:
- A reception centre has been set up at the British Council Library in Mumbai which will remain open overnight. The British Consulate in Mumbai has also deployed staff at the airport;
- The consulate has offered transport from the reception centre at the British Council offices to Mumbai airport. It has said it will help with arranging overnight accommodation near the airport and onward flights from Mumbai;
- British nationals who have lost their passports will be able to obtain emergency travel documents from the reception centre at the British Council offices, and from staff at Mumbai Airport from 0800 local time on the morning of 28 November. The Foreign Office has asked Indian authorities to fast-track exit visas for British nationals;
- It is offering advice on its UK in India website (www.ukinindia.org) and on the travel section of its www.fco.gov.uk site;
- Anyone worried about relatives or friends who are UK nationals in the affected area has been urged to call the Foreign and Commonwealth Office on + 44 020 7008 0000.