Romanian Prime Minister Victor Ponta on Wednesday announced his resignation over the club fire tragedy that claimed 30 lives.

"At least 90 people are in serious condition due to the incident that took place on October 6. Some of them are very critical," the authorities said.

Friday's mishap was the most serious in a public place in Romania for decades.

Thousands of people protested across Romania on Tuesday, demanding cabinet resignations as the death toll from a nightclub fire reached 32, with dozens more people in hospital critically hurt.

Angry about the way authorities grant permits and inspect public venues, protesters carried banners saying "Corruption Kills" and chanting "Murderers!" The disaster last weekend was one of the country's worst in decades.

In Bucharest, over 20,000 people marched to the government headquarters and the interior ministry, and protests spread out in the central Romanian cities of Brasov and Ploiesti. More rallies were being announced on Facebook across Romania in coming days.

The fire broke out on Friday night, when fireworks lit at a rock concert inside the Colectiv club set non-fireproofed insulation foam ablaze, triggering a stampede towards the single exit and trapping many of the roughly 400-strong audience inside.

In Bucharest, marchers shouted demands for Prime Minister Victor Ponta and deputy prime minister Gabriel Oprea to resign along with the mayor of the district where Colectiv is located.

Outside Colectiv, thousands of people laid a blanket of candles and flowers in remembrance.

Late on Tuesday, a Bucharest court decided to grant prosecutors a 30-day arrest warrant against the three owners of Colectiv, who were taken into custody on Monday on suspicion of manslaughter.

"All I can do is keep my head bowed before judgement," owner Costin Mincu said on Facebook through his lawyer, so far the only comment from any of the three men. "I regret what happened enormously."