Earlier in the week, some brokerages also reported slowness on their customer websites.

Several major US brokerage houses suffered technical glitches yesterday as their online infrastructure struggled to cope with the global market rout. 

A spokesperson for Fidelity, the investment manager with $2.2 trillion under management, said late Tuesday morning that intermittent technical creases had been ironed out on its website. Earlier in the morning, a message on the firm’s website read: “Our homepage is temporarily unavailable but don’t worry, we’re working quickly to fix this problem.”

TD Ameritrade said in a message on its website: "Due to volatile market conditions we are currently experiencing slowness on our web platform." It advised trying one of its mobile applications or a related company website.

Some took to Twitter to complain they were unable to access Merrill Edge, a brokerage website operated by Bank of America. A spokesman said in a statement: "Our systems remain operational. Some clients reported slowness logging into My Merrill and Merrill Edge due to unprecedented trading volume."

Robo-advice platforms - online money managers that use complex algorithms to determine asset allocation, usually to index-tracking funds – have yet to experience a serious market downturn like this week’s. Yesterday’s reported outages could prompt questions over whether such platforms are able to cope with extreme market volatility. 

On Monday, a few brokerages reported temporary issues or slowness on their client websites, including T Rowe Price and TD Ameritrade, which were later resolved. 

Fidelity had some temporary outages on its website in November that blocked customers from accessing their online accounts and offered free trades to compensate.