"Is there a surgeon free who can sew someone up?," a nurse cried out, bustling through the makeshift hospital ward.

"Is there anyone who can help?"

Behind her a team of volunteer doctors stood bent over a protester aged about 20, digging shrapnel from a stun grenade out of his leg and wrapping him in bandages.

On the bloodiest night of Kiev's three-month-long standoff, a steady flow of patients came through one of the last remaining field hospitals for injured anti-government protesters, this one housed in Kiev's iconic Mikhailovsky (St. Michael's) Orthodox Monastery.

Fierce clashes between protesters and police that have turned central Kiev into a war zone dragged on overnight as security forces pushed into the heart of the main opposition protest encampment on Kiev's Independence Square, or Maidan.

Demonstrators fought desperately to cling onto the square, which they have held since November, hurling Molotov cocktails and paving stones at police.

At least 25 people have died in the clashes with another 241 wounded and receiving treatment in hospital, the health ministry said Wednesday.

But doctors said many protesters were shunning official hospitals for fear of arrest.

As dawn broke over Kiev's battered city centre, dozens of injured or exhausted protesters lay in the main cathedral sleeping under blankets on the stone floor at the foot of the ornate golden iconostasis.

Across the courtyard, a dining room had been converted into a rudimentary surgery ward with room for 10 patients, and teams of medics were treating wounds as Orthodox saints peered down at them from the icons on the wall.

'We've been busy'

Volunteer Lena Liventsova, a doctor from Kiev, said she had been treating the injured for 24 hours without a break.

"How are our boys doing down there on the square?" she asked.

Liventsova said she had lost count of the number of wounded.

"We have been busy. You can see that most of the beds are still used," she said, pointing at other doctors working on patients.

Liventsova said the majority of wounds were from police grenades, but that people had also been treated for gunshot wounds, both from rubber bullets and live ammunition.

"For the moment we are OK for supplies but we are starting to run low on bandages," she said.

Mikhailovsky monastery -- perched on a hill near Independence Square -- has served on and off as one of the opposition's impromptu field hospitals since demonstrators first took refuge there when riot police tried to disperse student demonstrators back in November.

The makeshift treatment centre can perform only minor surgeries. But it became more important after fire yesterday gutted the last remaining opposition stronghold building on the Trade Union House on Independence Square, where the protest movement's main hospital was located.

US Ambassador to Kiev Geoffrey Pyatt said he stopped by on Wednesday morning and suspected the health ministry's toll did not include those in the monastery.

"Just did a quick check on the way in to work," he wrote on Twitter.

Volunteers working at the clinic like Olga Ivanenko, 31, a former journalist who had joined the ranks of the unpaid nurses, said they had come to help out after realising the scale of the latest violence.

"When I saw what was happening yesterday I decided I had to come to volunteer," she said, as an injured patient limped past.

The clinic was coping as well as it could and, with protesters and police still facing off, Ivanenko was ready for new arrivals.

"I haven't slept all night, but I still feel awake and ready to go," she said.