Yu, seen in a still from video footage of the dive, was at a depth of 15 metres when his oxygen supply was shut off.

A Chinese tourist has apologised for closing the valves on two divers' scuba tanks while they were diving on a group trip to the Philippines, saying it was "just a prank".

But one of the divers, who had to use his partner's oxygen tank when his supply was shut off, said he was seeking legal advice and may report the man to Chinese police, Yangtze Evening News reported on Monday.

The two separate incidents happened last week in waters off Puerto Galera, Mindoro, where the divers were on a group tour from China.

On Wednesday, one diver, surnamed Yu, suddenly had trouble breathing when he was at a depth of 15 metres and signalled to the instructor that he was in trouble, according to the report. The instructor gave Yu his backup tank and, after checking, reopened the valve.

"I didn't notice anything at the time when the tank valve was actually closed, but when I couldn't breathe I knew immediately that someone must have closed it," Yu told the newspaper.

He said another diver told him that she had seen a group member - identified as Tighe Lau, from Shanghai - later trying to tamper with Yu's scuba tank for a second time.

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According to Yu, Lau had threatened to close his scuba tank valve before they went diving, and after the incident he decided to join a different group the next day.

But Lau struck again on Thursday, closing the scuba tank valve of another diver, identified as Donghai, according to the report. The pair had apparently not met before the incident.

"We were about 10 metres down and he bumped into me several times as he was diving above me," Donghai said. "I didn't pay much attention at first, but then I suddenly couldn't breathe and I realised he had been trying to close the valve on my tank."

After using his partner's tank to breathe while the diver helped to reopen the valve, Donghai complained about Lau's behaviour to the group's instructor.

Lau apologised for his actions later that day, saying it was "just a prank done without thinking of the consequences", according to a screenshot of a group chat on social network WeChat.

But Yu told the newspaper he did not accept the explanation. "It's like stabbing someone with a knife and then saying it's a joke," he said.

On Friday, Lau again took to WeChat, saying in a post that he "apologised for shutting off the oxygen tanks and putting these two divers' lives in danger".

"I have apologised to both of them, and I now understand how idiotic my behaviour was and will take a lesson from this and strictly abide by the safety rules when I go diving in the future," he wrote.

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In response, Donghai told the newspaper that while he had not reported the incident to local police, he was following up with a lawyer in China.

The Chinese headquarters of scuba training agency SDI TDI ERDI said on Monday that it had no record of Lau obtaining a scuba diving licence, and it condemned any behaviour that endangered divers' safety. It was not known whether Lau had a valid diving licence from another training and certification agency.

The incidents have drawn outrage on Chinese social media.

"Who would accept such an apology?" one person wrote on microblog site Weibo, adding that it could even be seen as "attempted murder".

Another said: "This is not a joke. He is playing with someone else's life."

This article was first published in South China Morning Post.