A German diplomat was killed in the huge explosion in Beirut, the first confirmed German fatality, as the country's foreign minister expressed his condolences on Thursday over the tragedy.

"All of us at the foreign ministry are in deep mourning for our colleague," said Heiko Maas in a statement. He added that the female employee had died in her apartment in the Lebanese capital.

The news "confirmed our worst fears", the foreign minister said. The woman is the first German confirmed to have died as a result of the devastating explosion that obliterated much of Beirut port.

The provisional death toll from the massive blast stood at 137 Thursday, but with dozens missing and 5,000 wounded, the number of victims was expected to rise as rescue workers continued to comb through the rubble.

On Thursday, Maas also said that Germany would "not leave the people of Beirut in the lurch", as he pledged German support in the crisis. "The catastrophe may have reduced Beirut to rubble, but our friendship with Lebanon has not been shaken," he wrote in an article in Bild, Germany's most widely read daily newspaper.

The German government reportedly sent a 47-person team from its civil protection agency THW to Beirut on Wednesday, while the Germany army said it had medical vehicles in the area which "could be activated immediately".