Objective To investigate the delay in healthcare-seeking and diagnosis of imported malaria cases and identify their determinants in Hangzhou City from 2016 to 2024, so as to provide the scientific evidence for improving the management of imported malaria cases in Hangzhou City. Methods Malaria surveillance data and epidemiological case investigation forms reported in Hangzhou City from 2016 to 2024 were collected from Infectious Diseases Report Information Management System and Parasitic Diseases Prevention and Control Information Management System of Chinese Center for Disease Control and Prevention, including demographic characteristics, disease onset and healthcare-seeking, source of acquiring infections, previous medical history, treatment, and parasite species. All statistical analyses were conducted using the software SPSS 26.0. The determinants of delay in healthcare-seeking and diagnosis were identified using a univariate logistic regression model among imported malaria cases, and the association of delay in healthcare-seeking and diagnosis with severe malaria was examined using a multivariate logistic regression model. Results A total of 282 imported malaria cases were reported in Hangzhou City from 2016 to 2024, including 265 men (94.0%) and 17 women (6.0%), and there were 226 overseas labors (80.1%) and 271 African imported cases (96.1%). Most cases (40.8%, 115/282) initially sought healthcare services in district (county)-level medical institutions, and the misdiagnosis rate of initial healthcare-seeking was 22.7% (64/282). Among all reported cases, most acquired Plasmodium falciparum infections (74.8%, 211/282). The interval between disease onset and initial healthcare-seeking was 0 to 16 days, with 30.1% (85/282) of cases seeking healthcare on the day of disease onset. The interval between initial healthcare-seeking and definitive diagnosis was 0 to 46 days, with 38.6% (109/282) of the cases receiving definitive diagnosis on the day of healthcare-seeking. The proportions of cases with delays from disease onset to initial healthcare-seeking, from initial healthcare-seeking to definitive diagnosis, and from disease onset to definitive diagnosis were 13.1% (37/282), 28.4% (80/282), and 18.4% (52/282), respectively, and the percentages of cases with delay from disease onset to initial healthcare-seeking were 15.5% (9/58), 9.9% (7/71), 6.3% (5/79), and 21.6% (16/74) among cases under 30 years of age, at ages of 30 to 39 years, 40 to 49 years and 50 years and older (χ² = 8.843, P < 0.05). There were significant differences in the proportions of cases with delays from initial healthcare-seeking to definitive diagnosis in terms of sources of acquiring infections (χ² = 3.860, P < 0.05), levels of medical institutions for initial healthcare seeking (χ² = 19.768, P < 0.05), initial diagnosis results (χ² = 113.928, P < 0.05), and infected Plasmodium species (χ² = 13.030, P < 0.05), and there were significant differences in the proportions of cases with delays from disease onset to definitive diagnosis in terms of age groups (χ² = 9.211, P < 0.05), sources of acquiring infections (χ² = 5.554, P < 0.05), interval from disease onset to overseas travel history (χ² = 15.354, P < 0.05), initial diagnosis results (χ² = 54.830, P < 0.05), and infected Plasmodium species (χ² = 31.735, P < 0.05). Univariate logistic regression analysis identified age of 50 years and older as a risk factor for delay in healthcare-seeking (OR = 1.245, 95%CI: 1.085-1.708). Cases with an overseas travel history of more than 6 months prior to disease onset (OR = 3.057, 95%CI: 1.041-8.979), initial diagnosis as other diseases (OR = 29.405, 95%CI: 13.993-61.789), P. vivax infection (OR = 2.717, 95%CI: 1.016-7.266), and infection with other malaria parasite species (OR = 2.810, 95%CI: 1.498-5.273) were more likely to experience delay in diagnosis, and initial healthcare-seeking at province-level medical institutions was a protective factor for delay in diagnosis (OR = 0.135, 95%CI: 0.023-0.800). Of 282 imported malaria cases, there were 11 severe cases and deaths, including 10 P. falciparum malaria cases, and one P. ovale malaria case. Multivariate logistic regression analysis revealed that delay in diagnosis (OR = 6.285, 95%CI: 1.625-24.302) and overall delay (OR = 6.046, 95%CI: 1.491-24.522) were significantly associated with an increased risk of severe malaria. Conclusion There was a delay in healthcare-seeking and definitive diagnosis among imported malaria cases in Hangzhou City from 2016 to 2024, which was mainly attributed to age, place of overseas travel, level of medical institutions for initial healthcare-seeking, and Plasmodium species.