The Portuguese bank Espirito Santo, in Barcelona, Spain.

After a devastating day in the stock markets for Portugal's troubled lender Banco Espirito Santo (BES), analysts are weighing up whether the country's central bank could step in and bail out the bank.

Turmoil at the group which owns BES has embroiled the lender for months with top officials being suspended this week over suspected "harmful management." BES shares lost around 40 percent on Thursday after Portugal's largest listed lender by assets posted a first-half net loss of 3.58 billion euros ($4.8 billion). This effectively wiped out the 2.1 billion euro capital buffer it previously stated it had available.