WIESBADEN, Germany:At a loose end during Germany's first lockdown, the four Schwaderlapp sisters decided to put their long hours indoors to good use - by inventing a coronavirus board game that is selling by the thousands.

"Corona" can be played by up to four players, who compete to buy all the groceries on a shopping list for an elderly neighbour who is shielding against the virus.

The players collect and swap game cards, and the winner is whoever delivers all the items first. Hurdles along the way include encountering the virus, which sends you into quarantine, or finding that hoarders have already snapped up all the pasta or toilet rolls.

"The basic principle is one of solidarity," 20-year-old Sarah told Reuters TV from the family home in the western city of Wiesbaden.

"..But each of the players can decide to cooperate with the others ...or make thing harder for them by blocking their path with viruses."

The sisters worked on the game most evenings during the spring lockdown, gradually incorporating more elements from news broadcasts about the pandemic.

"That was the case with hoarding. And we saw about the balcony concerts in Italy and turned that into a playing card too," added sister Rebecca.

Impressed with his daughters' efforts, father Benedikt Schwaderlapp decided to commercialise the game by hiring an artist to design cards, board and box.

So far he's sold 2,000 copies, and signed up a toy store as a secondary distributor.

"Because the game has been so popular it's been quite a challenge for our family-based operation - packing and posting 500 games within a very short period," he said.

"Demand has been massive from across Germany."