At least two children were among those killed in the disaster, which happened on Friday when a length of roofing along the entrance to the station collapsed on a sunny day.
Rescuers worked into the night, using heavy construction machinery, to free the dead and wounded from under the rubble.
Serbian authorities inspected the train station the day after its roof collapsed. (AP PHOTO)
The station in the city about 70km northwest of Belgrade underwent renovations in 2021 and 2022.
Other minor works continued until July 2024 when the transport ministry said a total of 16 million euros ($A27 million) had been invested in the renovation.
Transport Minister Goran Vesic said on Saturday the inquiry, opened by prosecutors in Novi Sad, would include the state Traffic Institute, state railway company and the Chinese consortium that undertook the renovation work.
"The investigation will determine ... who made decisions and put seals and signatures, who was in charge of controlling the (quality of) works," Vesic said in a TV broadcast.
Vesic, state Serbian Railways company, the state Traffic Institute and the Chinese consortium - China Railway International Co Ltd and China Communications Construction Company, that renovated the building, all said on Friday that the part of the building that collapsed was not a part of the works.
Interior Minister Ivica Dacic said 20 people would be interviewed by authorities on Saturday in connection with the disaster, including people from the ministry in charge and the state railways operator.
"The documentation about the building will (also) be obtained ... about who made the decisions," Dacic added.
People brought flowers and tributes as the Serbian government declared a national day of mourning. (AP PHOTO)
Authorities declared Saturday a national day of mourning.
The University Clinical Center in Novi Sad said the three injured people remained in intensive care.
On Saturday morning, people brought flowers and toys, and lit candles near the site.
Workers were clearing away the last of the rubble.
"I am sorry about the people and we should make sure for something like this never to happen again," said Mane Gostovic, 75, a pensioner from Novi Sad.
Serbia's opposition, which accuses authorities loyal to President Aleksandar Vucic of rampant corruption, nepotism and excessive red tape, called for a protest in downtown Novi Sad later in the day.
Vucic, a populist, and his allies deny such allegations.
In a televised address late on Friday the president promised justice and demanded harsh punishment for those responsible.
