The bank tweeted early Friday afternoon that it was still "working to restore full service" Friday. The tweet said customers were still experiencing interruptions with some of its online applications, but did not say which ones.
The company blamed "technical difficulties" for the outage, which lasted one to two hours.
Maria Cenir from Scarborough in suburban Toronto told CBC News she first became aware of the issue while at a Royal Bank branch at 10:30.
A teller denied Cenir's request to take out money with a BMO card, because the system said she had no funds in her account.
Later, she went to a Petro-Canada station to fill up her gas tank, where she discovered her card was again declined — despite having the funds. The woman said she had to call her sister to come down with cash to pay for the gasoline.
The bank apologized to its clients for any inconvenience.
The bank has 925 branches across Canada.