At least 13 people have been killed in an explosion at a firecracker factory in India's southern state of Kerala, officials say.

The incident took place in Thrissur, where around 40 people were believed to be assembling firecrackers in a cluster of sheds for an upcoming festival. Several others were injured, with five reported to be in critical condition.

This was the second such incident this week. On Sunday, a blast at a firecracker factory in neighbouring Tamil Nadu state left at least 25 dead.

Accidental explosions are a grim routine in India's fireworks industry, recurring with troubling regularity - most visibly around Sivakasi in Tamil Nadu, which produces much of the country's supply.

The explosion in Thrissur on Tuesday around 15:30 local time (10:00 GMT) triggered secondary blasts that slowed rescue efforts. Firecrackers were being made in temporary sheds near paddy fields with poor road access, hampering emergency response.

The force of the blast was felt kilometres away - some residents mistook it for an earthquake - and nearby homes were damaged.

Eyewitnesses described chaotic scenes as locals joined rescue efforts, pulling out the injured and dead. Kerala's Revenue Minister K Rajan stated that all fireworks units preparing for the upcoming Thrissur Pooram - a major annual Hindu temple festival - had permission to manufacture and store fireworks in designated areas.

The workers were preparing fireworks for the Thiruvambady Temple, one of the two main participants in the climactic displays of the Thrissur Pooram. The festival's famed fireworks unfold in four phases, with the main overnight display drawing huge crowds.

While municipal chairman PN Surendran attributed the blast to high afternoon temperatures, officials said the cause remains unclear. A magisterial inquiry has been ordered to establish what happened and fix responsibility.

Kerala Chief Minister Pinarayi Vijayan has announced that medical experts from other states would be brought in to treat the burn victims if needed.

Prime Minister Narendra Modi has also announced financial assistance of 200,000 rupees ($2,137; £1,582) for the families of those who lost their lives, and 50,000 rupees for the injured.

Firecracker factory accidents are common in India due to highly volatile chemicals being handled in cramped, low-cost setups where even a small spark can trigger explosions. The industry, which is largely informal, has faced repeated scrutiny over safety standards.