Moscow said Wednesday it will review a new electronic permit system to regulate its coronavirus lockdown after large crowds formed in metros as police checked passes.

Moscow authorities began issuing digital permits to residents using cars or public transport this week in an effort to reduce isolation violations, with the system coming into effect Wednesday.

Following social media reports of crowds gathering in metro stations, Moscow Mayor Sergei Sobyanin acknowledged on Twitter that "queues formed in the metro".

He said he asked authorities responsible for checking the passes to "work in such a way that further inspections would not lead to a mass crowd of people."

In a second tweet, he said the crowds were cleared and that city authorities planned to implement "automatic" controls.

"We'll think about how to do this," he wrote.

News agency TASS reported that the congestion was caused by a lack of police to check permits.

Authorities say they have issued at least 3.2 million passes since Monday.

The permit system is being introduced against the backdrop of a sharp rise in the number of coronavirus infections in Russia, with officials reporting 3,388 new cases on Wednesday.

Health officials have recorded a total of 24,490 COVID-19 cases and 198 deaths.

Members of the armed services, municipal officials and journalists are among those exempt from the permit system.

Work passes will be valid until April 30, while passes obtained to go to a doctor or elsewhere can only be used once.

The digital permit system may be expanded to monitor people going out on foot even within their neighbourhood, if needed, authorities have said.

Moscow has been under lockdown since March 30, but is now struggling to cope with the influx of new cases and officials said that clinics were approaching their limits.