"Heathrow Airport can confirm that two aircraft were involved in an incident on the ground earlier this evening," the spokesman said.
"There are no reported injuries and passengers are in the process of being offloaded from the aircraft."
The aircraft, which collided while taxiing, included a British Airways Boeing 747 bound for Singapore, and a London Fire Brigade spokeswoman said the other airline involved in the collision was a Sri Lankan airlines Airbus A340.
The BA spokesman described the incident as a "minor collision", and added that an investigation had been launched.
"Our aircraft had a minor collision with another aircraft on the taxiways," the BA spokesman said.
"Engineers are inspecting the aircraft to ascertain the damage. The passengers have been offloaded and returned to the terminal building.
"We do not have any more precise details of the collision while it is being investigated.
"
He added that passengers were offered the option of a refund or a night