SATARA/BHUBANESWAR, INDIA -- India's COVID-19 vaccination drive was still facing some delays on Sunday after it hit a bump on the first day due to glitches in an app used to coordinate the campaign, according to officials in some states.

Prime Minister Narendra Modi launched on Saturday what his government has described as the "world's largest vaccination program." It aims to vaccinate around 300 million people to curb the pandemic in India, which has reported the second highest number of coronavirus cases after the United States.

India was aiming to vaccinate more than 300,000 people on Saturday, but only 191,181 people were inoculated on the first day, official data shows.

Many health workers, who were due to receive a vaccine on Saturday, did not get the message via an app developed by the government called Co-Win, officials in at least four states said. Officials in at least one state said the issues had still not been resolved on Sunday.

Co-Win is supposed to alert healthcare workers, who are first in line to get shots. It also allows officials to monitor and manage the entire program.

"We were planning to vaccinate 28,500 people on Saturday but could do only 18,328 because of glitches in the Co-Win app," a senior official at the health department of the western state of Maharashtra told Reuters on condition on anonymity.

Maharashtra, home to the financial hub of Mumbai, has been the Indian state hit hardest by COVID-19.

In the eastern states of Odisha and West Bengal, officials said they were forced to use printouts on Saturday due to issues with the app.

"We also went with our plan B and contacted people to be vaccinated directly offline," Bijay Kumar Mohapatra, director, Health Services, Odisha, told Reuters in the state capital Bhubaneswar.

The Indian government did not respond to a request for comment on Sunday.

"The system performance and speed was improved and is being further optimized," Manohar Agnani, a senior health ministry official, said on Saturday.

The eastern state of West Bengal was still encountering glitches on Sunday.

"The problem is yet to be fixed and we are facing serious impediments," said Dr. Ajoy Chakraborty, director of West Bengal health services.

Officials in other states could not be reached for comment on Sunday.

India is currently using Britain's Oxford University/AstraZeneca vaccine, which is also being produced in India, and a government-backed vaccine developed by India's Bharat Biotech.

However, approval of Bharat Biotech's COVAXIN has been criticized by health experts and opposition lawmakers due to a lack of efficacy data, which the manufacturer is still conducting.

Additional reporting by Sumit Khanna in Ahmedabad and Subrata Nagchoudhury in Kolkata Editing by Himani Sarkar and Susan Fenton