When the terrorists stormed the building, he and a group of people were ushered into the kitchen. Chamberlain told Sky News that one of the waiters was shot in the arm.
"They were talking about Britons and Americans specifically. They shot people completely unnecessarily," he said.
The group of about 30 to 40 people were then "marched up like sheep" by a "young guy with a sub-machine gun, who was about 22-23."
The gunman then told people to stop and asked them to put their hands up. The attacker asked if any of the people were British or Americans.
Chamberlain said: "My Indian friend told me 'don't be a hero' and tell him you're Italian
Chamberlain said he got to about the 18th floor of the hotel and there was a gunman below them, and there were gunshots above and smoke everywhere.
The Briton and another person managed to sneak out of a fire door "without the gunman seeing us", where they stayed for about 15 minutes.
"I phoned my girlfriend and told her I loved her and thought it would be the last time I would talk to anyone," Chamberlain said.
He then walked "slowly downstairs expecting to see somebody with a gun around the corner" but they had gone.
He then smashed a window. He said: "the smoke was so thick I thought we were going to suffocate".
Chamberlain said he walked into the lobby and when he came out into the street there were about 20 police officers there "looking just as scared as any of us" and a few fire engines.