* Nationalities of victims not yet clear
* Three detained in criminal investigation
* Mayor says other apartments likely used as hostels
* Says they must be identified and shut down (Add three people detained, witness quote, other detail)
By Andrius Sytas and Janis Laizans
RIGA, April 28 (Reuters) - Eight people died in a fire in a cramped, "illegal" tourist hostel in the centre of the Latvian capital Riga early on Wednesday and the city's mayor vowed to shut down such accommodation.
Three people were detained as police launched a criminal investigation, the Latvian news agency BNS said.
Mayor Martins Stakis said the hostel, set up in an apartment near Riga's main railway station, was mainly used by foreigners but it was not clear yet who the victims were.
Alongside the eight dead, nine people were found injured and 24 evacuated from the fire on the sixth floor after emergency services were summoned at 4.43 a.m. (0143 GMT), a Fire and Rescue service statement said.
"I was woken by an explosion and saw an orange light shining beneath the door," a visibly shaken witness identified only as Viktorija told the public broadcaster's live programme outside the building.
"I crawled out on my knees. My airways are burnt and the ambulance said I need a doctor, but I think others need them more," she said.
One person was found dead at the hostel on Tuesday, before the fire, after a suspected drug overdose, LETA news agency reported, citing authorities.
The mayor said the hostel was called Japanese Style Centrum. Pictures of its premises on booking.com website show beds tightly packed into small attic rooms.
"Rooms looked like a shoe box," Sofia from Spain wrote in a review on the website after staying in the hostel in February.
Another review, by a Latvian called Viktorija who stayed there in March, said the room had no window and no ventilation, while others spoke of long-term residents living alongside visiting tourists.
"People sleeping in the stairs," an anonymous reviewer from Australia wrote in December. The hostel did not immediately respond to questions sent via the website inquiry form.
Officials were refused entry in February to carry out a fire safety inspection, Interior Minister Sandis Girgens said, while Stakis described the hostel as "illegal".
"This was not a (real) hostel, this was an apartment that was used as a hostel," the mayor said. "It is very likely that this is not the only such apartment in Riga, and we must fix this."
Hotels and hostels in the picturesque Baltic state have remained free to operate throughout the COVID-19 pandemic but numbers of foreign visitors have dropped sharply. The nation of 1.9 million has reported 2,106 deaths from the virus, with daily cases rising recently but still well below January's peak.