According to Official Guinness Records,
At an air-raid shelter in Chongqing, China c. 4,000 people were killed on 6 Jun 1941. The crowd were leaving the shelter after an air-raid when the warning siren sounded again. The 4000 deaths were due to suffocation and trampling as the crowd tried to return to the shelter.
For a complete list of 1941 records, please visit 1941 Guinness Records in China.