At least five Britons were killed in an attack in Tunisia on Friday, British Foreign Secretary Philip Hammond said.

Dozens of people, including foreign tourists, were killed when at least one gunman opened fire on a Tunisian beachside hotel in the popular resort of Sousse on Friday, according to Tunisia's Interior Ministry.

The victim toll grew to 37 killed, 36 injured, in the deadly hotel attack, said the Tunisian Ministry of Health.

After chairing an emergency meeting in London, Hammond said on national TV "The situation on the ground is still somewhat confused and we can't be sure exactly how many, but because of the nature of the composition of the tourist population in this part of Tunisia we have to assume that a high proportion of those killed and injured will have been British."

He also warned the death toll of British nationals in the attack could rise.