The COVID‐19 pandemic led to potential delays in diagnosis and treatment of cancer patients, which may negatively affect the prognosis of these patients. This study aimed to quantify the impact of COVID‐19 on the short‐term survival of cancer patients by comparing a period of four months after the outbreak began (2 March 2020) with an equal period from 2019. All cancer cases of the esophagus, stomach, colon and rectum, pancreas, lung, skin‐melanoma, breast, cervix, and prostate, from the Portuguese Oncology Institute of Porto (IPO‐Porto) and diagnosed between 2 March and 1 July of 2019 (before COVID‐19) and 2020 (after COVID‐19) were identified. Information regarding sociodemographic, clinical and treatment characteristics were collected from the cancer registry database and clinical files. Vital status was assessed to 31 October of the respective years. Cox proportional hazards regression was used to estimate crude and propensity score‐adjusted hazards ratio (HR) and 95% confidence intervals (95%CI) of death. During follow‐up to October 31, there were 154 (11.8%) deaths observed before COVID‐19 and 131 (17.2%) after COVID‐19, corresponding to crude and adjusted HRs (95%CI) of 1.51 (1.20‐1.91) and 1.10 (0.86‐1.40), respectively. Significantly higher adjusted hazards of death were observed for patients with stage III cancer (HR=2.37; 95%C:1.14‐4.94) and those undergoing surgical treatment (HR=3.97; 95%CI:1.14‐13.77), while patients who did not receive any treatment had a lower mortality hazards (HR=0.62; 95%CI:0.46‐0.83). The higher overall short‐term mortality observed during the COVID‐19 pandemic largely reflects the effects of the epidemic on the case‐mix of patients being diagnosed with cancer.