Hong Kong police seized explosives and arrested nine members of a radical political group on Monday, including a student and a teaching assistant, media in the city reported.

The arrests come ahead of a crucial vote on political reform in Hong Kong this week that has split the former British colony and triggered widespread protests.

It was not immediately clear if the explosives and arrests were linked to the vote. A police spokeswoman declined to confirm the reports or to provide an official statement.

The explosives seized were triacetone triperoxide (TATP), according to a report in the South China Morning Post, which cited a police source. TATP has been used in attacks by extremists in Israel and London.

Police also seized chemical substances that could be used to make explosives and air guns at some of the suspects' homes, according to reports that were also carried on broadcasters RTHK and Cable TV.

Hong Kong lawmakers are due to vote by the end of the week on how the city will select its next chief executive in 2017. Beijing has proposed a direct vote for pre-screened, pro-Beijing candidates, which pro-democracy lawmakers have vowed to veto.

The issue led to mainly peaceful street protests last year that lasted for 79 days and, at their height, included more than 100,000 people.

(Reporting by Bobby Yip, Tyrone Siu, Yimou Lee, Donny Kwok and Clare Baldwin; Editing by Anne Marie Roantree and Paul Tait)