A coronavirus surge sweeping through Thailand's prisons has thrown the spotlight on the kingdom's overcrowded penal system, where some inmates have less space to sleep than the inside of a coffin, AFP reports.

Almost 25,000 people have tested positive inside jails, where inmates living cheek by jowl have been encouraged to keep wearing their masks even while they sleep.

Authorities have floated plans to give early releases to prisoners with underlying medical conditions and have announced funding for more testing and medical care in recent days.

But former inmates say those behind bars have been kept in the dark about the seriousness of the outbreak.