A 30-year-old homeless man has been charged with attempted murder after a senior was stabbed in the chest in a downtown Vancouver coffee shop Wednesday afternoon.

Charged is Mohamed Amer, believed to be from Ottawa.

Vancouver police say the 71-year-old victim was sitting by himself at the Waves coffee shop on the 400 block of West Hastings Street near the downtown SFU campus when a man not known to him sat down next to him.

"Suddenly and without provocation or anything being said, the unknown man allegedly took a knife and stabbed the elderly man in the chest," said Const. Lindsey Houghton.

As customers rushed to help the man, the attacker simply waited for police to arrive, Houghton said.

The senior is in critical condition in hospital.

Police are referring Amer for a psychiatric assessment.

The attack comes as police in Surrey announce the arrest of a 19-year-old suspect in two apparent random attacks on TransLink buses in recent days.