Lisbon -Lisbon stock market authorities on Thursday suspended trading in Banco Espirito Santo until 11:00 after the stricken Portuguese bank announced historic losses.
BES posted first-half losses of $4.78bn late on Wednesday.
This was the biggest loss ever reported by a bank in Portugal, due to exposure to the debts of its parent, Espirito Santo Group.
Stock market authorities said the suspension was intended to give investors time to "analyse the statements" from the bank, the biggest private bank in Portugal.
The result, which had been widely anticipated by investors, contrasts with a loss of €237m in the first half of 2013.
The bank also announced provisions for bad debts and unforseen costs totalling €4.25bn. BES revised its direct exposure to Espirito Santo's debt upwards to €1.57bn, including insurance costs.
It had previously said it was exposed to €1.2bn of its parent group's liabilities.
The difficulties in the Espirito Santo group of companies surfaced earlier this year, denting confidence in Portugal's future after it exited a €78bn EU-IMF debt rescue programme.