Britain's Queen Elizabeth II said she was "deeply shocked" by a wave of terrorist attacks on London Underground trains and a bus, and sent her sympathy to those affected.

"The dreadful events in London this morning have deeply shocked us all," the Queen said in a statement.

"I know I speak for the whole nation in expressing my sympathy for all those affected, the relatives of the killed and injured," she said.

"I have nothing but admiration for the emergency services as they go about their work."