The group of men wearing masks and speaking French to each other broke the casino doors with a hammer and entered shooting into the air.
"Even though the criminals fired several shots, fortunately no one was hurt,” said the Basel prosecutor in a statement. “However, some clients and security personnel were slightly injured after being knocked around by the criminals.”
They ordered the 600 clients and employees inside to lie on the ground while they tried to break into safes in the basement and emptied cash out of the registered.
They left in two cars with French license plates from the Bas-Rhin region, according to the French authorities. They crossed the Franco-Swiss border at Flughafenstrasse, which borders the Basel-Mulhouse airport.
"How these criminals were able to leave Flughafenstrasse, which is on French soil, is will be investigated jointly with the French authorities, the Swiss statement said.
On 19 March police arrested a French man living in Germany for the armed robber of a casino in Geneva two weeks ago.