Nov 9 (Reuters) - Customers of financial services firms Merrill Lynch, Fidelity, Charles Schwab Corp, TD Ameritrade and Vanguard faced difficulties logging in or placing orders on Monday, according to outage monitoring website Downdetector.com.

Brokerages have faced a massive surge in trading volumes after the first successful data from a large-scale clinical trial of a coronavirus vaccine earlier in the day.

It was not immediately clear what caused the outages.

"Some Schwab applications experienced technical issues early this morning, which have now been resolved. We are currently working to address client questions as quickly as possible," Charles Schwab said in a tweet https://twitter.com/CharlesSchwab/status/1325843864666705920.

TD Ameritrade also said https://twitter.com/TDAmeritrade/status/1325866116527378432 that the company had resolved the issue that affected some clients' ability to log in across multiple TDA platforms due to unprecedented volumes of activity. (Reporting by Noor Zainab Hussain in Bengaluru; Editing by Vinay Dwivedi and Shailesh Kuber)