Russian forces have entered the largest hospital in the southern Ukrainian city of Mariupol and are preventing doctors and patients from leaving the building, the city's deputy mayor says.

Sergei Orlov told the BBC about 400 people at the Regional Intensive Care Hospital had been taken "hostages".

For nearly two weeks, the city has been surrounded by Russian troops with gas, running water and electricity cut off.

Local authorities say at least 2,500 deaths have been confirmed in the city.

"We received information that the Russian army captured our biggest hospital," Mr Orlov said.

In a post on Facebook, the governor of Donetsk region, Pavlo Kirilenko, said a hospital worker had managed to alert the authorities about the situation.

The hospital, he said, was the same that was damaged by a Russian strike last week.

Mariupol is the centre of a growing humanitarian crisis, as food and medical supplies run out and aid is not being allowed in. The city has been under constant Russian shelling, with an estimated 350,000 residents trapped.

On Tuesday, about 2,000 cars left Mariupol, the local council said, and 2,000 others were waiting to leave. But no aid was allowed in.